testing: improve test children API

This changeset results from the discussion in and fixes #126987.
Migration for these changes should take about 15-20 minutes.

- `createTestItem` no longer takes a parent. Instead, it creates a free-
  floating test item, which can be added as a child of a parent.
- The `TestItem.children` is now a `TestItemCollection`, a set-like
  interface that also allows replacing items (intelligently diffing
	them internally) wholesale. This removes the need for the "generation
	counter" used in samples previously.
- There is no longer a `root` on the test controller, but instead an
  `items` property which is the same `TestItemCollection`
- The `tests` in the `TestRunRequest` has been replaced with an `include`
  property. If undefined, the extension should run all tests. (Since
	there is no longer a root to reference).

Here's some example migrations:

- https://github.com/microsoft/vscode-extension-samples/commit/3fad3d66c110107946f827daedd7759cad7c4358
- https://github.com/microsoft/vscode-selfhost-test-provider/commit/3aff74631605dfd4120b98014f54ff744f292fe0

.vscode/launch.json

@@ -198,6 +198,7 @@
 			"type": "pwa-chrome",
 			"request": "launch",
 			"name": "Launch VS Code Internal",
+			"trace": true,
 			"windows": {
 				"runtimeExecutable": "${workspaceFolder}/scripts/code.bat"
 			},

src/vs/vscode.proposed.d.ts

@@ -1788,6 +1788,16 @@ declare module 'vscode' {
 		 */
 		export function createTestObserver(): TestObserver;
 
+		/**
+		 * Creates a new managed {@link TestItem} instance. It can be added into
+		 * the {@link TestItem.children} of an existing item, or into the
+		 * {@link TestController.items}.
+		 * @param id Unique identifier for the TestItem.
+		 * @param label Human-readable label of the test item.
+		 * @param uri URI this TestItem is associated with. May be a file or directory.
+		 */
+		export function createTestItem(id: string, label: string, uri?: Uri): TestItem;
+
 		/**
 		 * List of test results stored by the editor, sorted in descending
 		 * order by their `completedAt` time.
@@ -1937,8 +1947,8 @@ declare module 'vscode' {
 		label: string;
 
 		/**
-		 * Root test item. Tests in the workspace should be added as children of
-		 * the root. The extension controls when to add these, although the
+		 * Available test items. Tests in the workspace should be added in this
+		 * collection. The extension controls when to add these, although the
 		 * editor may request children using the {@link resolveChildrenHandler},
 		 * and the extension should add tests for a file when
 		 * {@link vscode.workspace.onDidOpenTextDocument} fires in order for
@@ -1948,9 +1958,7 @@ declare module 'vscode' {
 		 * as files change. See  {@link resolveChildrenHandler} for details around
 		 * for the lifecycle of watches.
 		 */
-		// todo@API a little weird? what is its label, id, busy state etc? Can I dispose this?
-		// todo@API allow createTestItem-calls without parent and simply treat them as root (similar to createSourceControlResourceGroup)
-		readonly root: TestItem;
+		readonly items: TestItemCollection;
 
 		/**
 		 * Creates a configuration used for running tests. Extensions must create
@@ -1962,28 +1970,11 @@ declare module 'vscode' {
 		 */
 		createRunConfiguration(label: string, group: TestRunConfigurationGroup, runHandler: TestRunHandler, isDefault?: boolean): TestRunConfiguration;
 
-		/**
-		 * Creates a new managed {@link TestItem} instance as a child of this
-		 * one.
-		 * @param id Unique identifier for the TestItem.
-		 * @param label Human-readable label of the test item.
-		 * @param parent Parent of the item. This is required; top-level items
-		 * should be created as children of the {@link root}.
-		 * @param uri URI this TestItem is associated with. May be a file or directory.
-		 * @param data Custom data to be stored in {@link TestItem.data}
-		 */
-		createTestItem(
-			id: string,
-			label: string,
-			parent: TestItem,
-			uri?: Uri,
-		): TestItem;
-
 		/**
 		 * A function provided by the extension that the editor may call to request
 		 * children of a test item, if the {@link TestItem.canExpand} is `true`.
 		 * When called, the item should discover children and call
-		 * {@link TestController.createTestItem} as children are discovered.
+		 * {@link vscode.test.createTestItem} as children are discovered.
 		 *
 		 * The item in the explorer will automatically be marked as "busy" until
 		 * the function returns or the returned thenable resolves.
@@ -2030,11 +2021,12 @@ declare module 'vscode' {
 	 */
 	export class TestRunRequest {
 		/**
-		 * Array of specific tests to run. The controllers should run all of the
-		 * given tests and all children of the given tests, excluding any tests
-		 * that appear in {@link TestRunRequest.exclude}.
+		 * Filter for specific tests to run. If given, the extension should run all
+		 * of the given tests and all children of the given tests, excluding
+		 * any tests that appear in {@link TestRunRequest.exclude}. If this is
+		 * not given, then the extension should simply run all tests.
 		 */
-		tests: TestItem[];
+		include?: TestItem[];
 
 		/**
 		 * An array of tests the user has marked as excluded in the editor. May be
@@ -2051,11 +2043,11 @@ declare module 'vscode' {
 		configuration?: TestRunConfiguration;
 
 		/**
-		 * @param tests Array of specific tests to run.
+		 * @param tests Array of specific tests to run, or undefined to run all tests
 		 * @param exclude Tests to exclude from the run
 		 * @param configuration The run configuration used for this request.
 		 */
-		constructor(tests: readonly TestItem[], exclude?: readonly TestItem[], configuration?: TestRunConfiguration);
+		constructor(include?: readonly TestItem[], exclude?: readonly TestItem[], configuration?: TestRunConfiguration);
 	}
 
 	/**
@@ -2115,6 +2107,34 @@ declare module 'vscode' {
 		end(): void;
 	}
 
+	/**
+	 * Collection of test items, found in {@link TestItem.children} and
+	 * {@link TestController.items}.
+	 */
+	export interface TestItemCollection {
+		/**
+		 * A read-only array of all the test items children. Can be retrieved, or
+		 * set in order to replace children in the collection.
+		 */
+		all: readonly TestItem[];
+
+		/**
+		 * Adds the test item to the children. If an item with the same ID already
+		 * exists, it'll be replaced.
+		 */
+		add(item: TestItem): void;
+
+		/**
+		 * Removes the a single test item from the collection.
+		 */
+		remove(itemId: string): void;
+
+		/**
+		 * Efficiently gets a test item by ID, if it exists, in the children.
+		 */
+		get(itemId: string): TestItem | undefined;
+	}
+
 	/**
 	 * A test item is an item shown in the "test explorer" view. It encompasses
 	 * both a suite and a test, since they have almost or identical capabilities.
@@ -2135,12 +2155,12 @@ declare module 'vscode' {
 		/**
 		 * A mapping of children by ID to the associated TestItem instances.
 		 */
-		//todo@API use array over es6-map
-		readonly children: ReadonlyMap<string, TestItem>;
+		readonly children: TestItemCollection;
 
 		/**
-		 * The parent of this item, given in {@link TestController.createTestItem}.
-		 * This is undefined only for the {@link TestController.root}.
+		 * The parent of this item, given in {@link vscode.test.createTestItem}.
+		 * This is undefined top-level items in the `TestController`, and for
+		 * items that aren't yet assigned to a parent.
 		 */
 		readonly parent?: TestItem;
 
@@ -2193,11 +2213,6 @@ declare module 'vscode' {
 		 * Extensions should generally not override this method.
 		 */
 		invalidateResults(): void;
-
-		/**
-		 * Removes the test and its children from the tree.
-		 */
-		dispose(): void;
 	}
 
 	/**

src/vs/workbench/api/common/extHost.api.impl.ts

@@ -346,6 +346,10 @@ export function createApiFactoryAndRegisterActors(accessor: ServicesAccessor): I
 				checkProposedApiEnabled(extension);
 				return extHostTesting.createTestController(provider, label);
 			},
+			createTestItem(id, label, uri) {
+				checkProposedApiEnabled(extension);
+				return extHostTesting.createTestItem(id, label, uri);
+			},
 			createTestObserver() {
 				checkProposedApiEnabled(extension);
 				return extHostTesting.createTestObserver();

src/vs/workbench/api/common/extHostTesting.ts

@@ -3,7 +3,6 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
-import { mapFind } from 'vs/base/common/arrays';
 import { RunOnceScheduler } from 'vs/base/common/async';
 import { VSBuffer } from 'vs/base/common/buffer';
 import { CancellationToken, CancellationTokenSource } from 'vs/base/common/cancellation';
@@ -19,19 +18,22 @@ import { generateUuid } from 'vs/base/common/uuid';
 import { ExtHostTestingShape, MainContext, MainThreadTestingShape } from 'vs/workbench/api/common/extHost.protocol';
 import { ExtHostCommands } from 'vs/workbench/api/common/extHostCommands';
 import { IExtHostRpcService } from 'vs/workbench/api/common/extHostRpcService';
+import { TestItemImpl } from 'vs/workbench/api/common/extHostTestingPrivateApi';
 import * as Convert from 'vs/workbench/api/common/extHostTypeConverters';
-import { TestItemImpl, TestRunConfigurationGroup, TestRunRequest } from 'vs/workbench/api/common/extHostTypes';
+import { TestRunConfigurationGroup, TestRunRequest } from 'vs/workbench/api/common/extHostTypes';
 import { SingleUseTestCollection, TestPosition } from 'vs/workbench/contrib/testing/common/ownedTestCollection';
 import { AbstractIncrementalTestCollection, CoverageDetails, IFileCoverage, IncrementalChangeCollector, IncrementalTestCollectionItem, InternalTestItem, ISerializedTestResults, ITestIdWithSrc, ITestItem, RunTestForControllerRequest, TestRunConfigurationBitset, TestsDiff } from 'vs/workbench/contrib/testing/common/testCollection';
 import type * as vscode from 'vscode';
 
+interface ControllerInfo {
+	controller: vscode.TestController,
+	configurations: Map<number, vscode.TestRunConfiguration>,
+	collection: SingleUseTestCollection,
+}
+
 export class ExtHostTesting implements ExtHostTestingShape {
 	private readonly resultsChangedEmitter = new Emitter<void>();
-	private readonly controllers = new Map</* controller ID */ string, {
-		controller: vscode.TestController,
-		configurations: Map<number, vscode.TestRunConfiguration>,
-		collection: SingleUseTestCollection,
-	}>();
+	private readonly controllers = new Map</* controller ID */ string, ControllerInfo>();
 	private readonly proxy: MainThreadTestingShape;
 	private readonly runTracker: TestRunCoordinator;
 	private readonly observer: TestObservers;
@@ -61,12 +63,13 @@ export class ExtHostTesting implements ExtHostTestingShape {
 		const proxy = this.proxy;
 
 		const controller: vscode.TestController = {
-			root: collection.root,
+			items: collection.root.children,
 			get label() {
 				return label;
 			},
 			set label(value: string) {
 				label = value;
+				collection.root.label = value;
 				proxy.$updateControllerLabel(controllerId, label);
 			},
 			get id() {
@@ -85,14 +88,7 @@ export class ExtHostTesting implements ExtHostTestingShape {
 				return config;
 			},
 			createTestRun: (request, name, persist = true) => {
-				return this.runTracker.createTestRun(controllerId, request, name, persist);
-			},
-			createTestItem(id: string, label: string, parent: vscode.TestItem, uri: vscode.Uri, data?: unknown) {
-				if (!(parent instanceof TestItemImpl)) {
-					throw new Error(`The "parent" passed in for TestItem ${id} is invalid`);
-				}
-
-				return new TestItemImpl(id, label, uri, data, parent);
+				return this.runTracker.createTestRun(controllerId, collection, request, name, persist);
 			},
 			set resolveChildrenHandler(fn) {
 				collection.resolveHandler = fn;
@@ -108,10 +104,14 @@ export class ExtHostTesting implements ExtHostTestingShape {
 			},
 		};
 
+		// back compat:
+		(controller as any).createTestITem = this.createTestItem.bind(this);
+
 		proxy.$registerTestController(controllerId, label);
 		disposable.add(toDisposable(() => proxy.$unregisterTestController(controllerId)));
 
-		this.controllers.set(controllerId, { controller, collection, configurations });
+		const info: ControllerInfo = { controller, collection, configurations };
+		this.controllers.set(controllerId, info);
 		disposable.add(toDisposable(() => this.controllers.delete(controllerId)));
 
 		disposable.add(collection.onDidGenerateDiff(diff => proxy.$publishDiff(controllerId, diff)));
@@ -119,6 +119,13 @@ export class ExtHostTesting implements ExtHostTestingShape {
 		return controller;
 	}
 
+	/**
+	 * Implements vscode.test.createTestItem
+	 */
+	public createTestItem(id: string, label: string, uri?: vscode.Uri) {
+		return new TestItemImpl(id, label, uri);
+	}
+
 	/**
 	 * Implements vscode.test.createTestObserver
 	 */
@@ -136,26 +143,19 @@ export class ExtHostTesting implements ExtHostTestingShape {
 			throw new Error('The request passed to `vscode.test.runTests` must include a configuration');
 		}
 
-		if (!req.tests.length) {
-			return;
+		const controller = this.controllers.get(config.controllerId);
+		if (!controller) {
+			throw new Error('Controller not found');
 		}
 
-		const testListToProviders = (tests: ReadonlyArray<vscode.TestItem>) =>
-			tests
-				.map(this.getInternalTestForReference, this)
-				.filter(isDefined)
-				.map(t => ({ controllerId: t.controllerId, testId: t.item.extId, configId: config }));
-
 		await this.proxy.$runTests({
 			targets: [{
-				testIds: req.tests.map(t => t.id),
+				testIds: req.include?.map(t => t.id) ?? [controller.collection.root.id],
 				profileGroup: configGroupToBitset[config.group],
 				profileId: config.configId,
 				controllerId: config.controllerId,
 			}],
-			exclude: req.exclude
-				? testListToProviders(req.exclude).map(t => ({ testId: t.testId, controllerId: t.controllerId }))
-				: undefined,
+			exclude: req.exclude?.map(t => ({ testId: t.id, controllerId: config.controllerId })),
 		}, token);
 	}
 
@@ -252,7 +252,11 @@ export class ExtHostTesting implements ExtHostTestingShape {
 			configuration,
 		);
 
-		const tracker = this.runTracker.prepareForMainThreadTestRun(publicReq, TestRunDto.fromInternal(req), token);
+		const tracker = this.runTracker.prepareForMainThreadTestRun(
+			publicReq,
+			TestRunDto.fromInternal(req, lookup.collection),
+			token,
+		);
 
 		try {
 			await configuration.runHandler(publicReq, token);
@@ -275,14 +279,6 @@ export class ExtHostTesting implements ExtHostTestingShape {
 			this.runTracker.cancelRunById(runId);
 		}
 	}
-
-	/**
-	 * Gets the internal test item associated with the reference from the extension.
-	 */
-	private getInternalTestForReference(test: vscode.TestItem) {
-		return mapFind(this.controllers.values(), ({ collection }) => collection.getTestByReference(test))
-			?? this.observer.getMirroredTestDataByReference(test);
-	}
 }
 
 class TestRunTracker extends Disposable {
@@ -396,7 +392,7 @@ export class TestRunCoordinator {
 	/**
 	 * Implements the public `createTestRun` API.
 	 */
-	public createTestRun(controllerId: string, request: vscode.TestRunRequest, name: string | undefined, persist: boolean): vscode.TestRun {
+	public createTestRun(controllerId: string, collection: SingleUseTestCollection, request: vscode.TestRunRequest, name: string | undefined, persist: boolean): vscode.TestRun {
 		const existing = this.tracked.get(request);
 		if (existing) {
 			return existing.createRun(name);
@@ -404,14 +400,14 @@ export class TestRunCoordinator {
 
 		// If there is not an existing tracked extension for the request, start
 		// a new, detached session.
-		const dto = TestRunDto.fromPublic(controllerId, request);
+		const dto = TestRunDto.fromPublic(controllerId, collection, request);
 		const config = tryGetConfigFromTestRunReq(request);
 		this.proxy.$startedExtensionTestRun({
 			controllerId,
 			config: config && { group: configGroupToBitset[config.group], id: config.configId },
 			exclude: request.exclude?.map(t => t.id) ?? [],
 			id: dto.id,
-			tests: request.tests.map(t => t.id),
+			include: request.include?.map(t => t.id) ?? [collection.root.id],
 			persist
 		});
 
@@ -441,41 +437,44 @@ const tryGetConfigFromTestRunReq = (request: vscode.TestRunRequest) => {
 };
 
 export class TestRunDto {
-	public static fromPublic(controllerId: string, request: vscode.TestRunRequest) {
+	public static fromPublic(controllerId: string, collection: SingleUseTestCollection, request: vscode.TestRunRequest) {
 		return new TestRunDto(
 			controllerId,
 			generateUuid(),
-			new Set(request.tests.map(t => t.id)),
+			request.include && new Set(request.include.map(t => t.id)),
 			new Set(request.exclude?.map(t => t.id) ?? Iterable.empty()),
+			collection,
 		);
 	}
 
-	public static fromInternal(request: RunTestForControllerRequest) {
+	public static fromInternal(request: RunTestForControllerRequest, collection: SingleUseTestCollection) {
 		return new TestRunDto(
 			request.controllerId,
 			request.runId,
-			new Set(request.testIds),
+			request.testIds.includes(collection.root.id) ? undefined : new Set(request.testIds),
 			new Set(request.excludeExtIds),
+			collection,
 		);
 	}
 
 	constructor(
 		public readonly controllerId: string,
 		public readonly id: string,
-		private readonly include: ReadonlySet<string>,
+		private readonly include: ReadonlySet<string> | undefined,
 		private readonly exclude: ReadonlySet<string>,
+		public readonly colllection: SingleUseTestCollection,
 	) { }
 
 	public isIncluded(test: vscode.TestItem) {
 		for (let t: vscode.TestItem | undefined = test; t; t = t.parent) {
-			if (this.include.has(t.id)) {
+			if (this.include?.has(t.id)) {
 				return true;
 			} else if (this.exclude.has(t.id)) {
 				return false;
 			}
 		}
 
-		return false;
+		return this.include === undefined; // default to true if running all tests with include=undefined
 	}
 }
 
@@ -624,6 +623,12 @@ class TestRunImpl implements vscode.TestRun {
 			test = test.parent;
 		}
 
+		const root = this.#req.colllection.root;
+		if (!sent.has(root.id)) {
+			sent.add(root.id);
+			chain.unshift(Convert.TestItem.from(root));
+		}
+
 		this.#proxy.$addTestsToRun(this.#req.controllerId, this.#req.id, chain);
 	}
 }

src/vs/workbench/api/common/extHostTestingPrivateApi.ts

@@ -3,26 +3,50 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
-import { Emitter } from 'vs/base/common/event';
-import { TestItemImpl } from 'vs/workbench/api/common/extHostTypes';
 import * as vscode from 'vscode';
 
-export const enum ExtHostTestItemEventType {
-	NewChild,
-	Disposed,
+export const enum ExtHostTestItemEventOp {
+	Upsert,
+	RemoveChild,
 	Invalidated,
 	SetProp,
+	Bulk,
+}
+
+export interface ITestItemUpsertChild {
+	op: ExtHostTestItemEventOp.Upsert;
+	item: TestItemImpl;
+}
+
+export interface ITestItemRemoveChild {
+	op: ExtHostTestItemEventOp.RemoveChild;
+	id: string;
+}
+
+export interface ITestItemInvalidated {
+	op: ExtHostTestItemEventOp.Invalidated;
+}
+
+export interface ITestItemSetProp {
+	op: ExtHostTestItemEventOp.SetProp;
+	key: keyof vscode.TestItem;
+	value: any;
+}
+export interface ITestItemBulkReplace {
+	op: ExtHostTestItemEventOp.Bulk;
+	ops: (ITestItemUpsertChild | ITestItemRemoveChild)[];
 }
 
 export type ExtHostTestItemEvent =
-	| [evt: ExtHostTestItemEventType.NewChild, item: TestItemImpl]
-	| [evt: ExtHostTestItemEventType.Disposed]
-	| [evt: ExtHostTestItemEventType.Invalidated]
-	| [evt: ExtHostTestItemEventType.SetProp, key: keyof vscode.TestItem, value: any];
+	| ITestItemUpsertChild
+	| ITestItemRemoveChild
+	| ITestItemInvalidated
+	| ITestItemSetProp
+	| ITestItemBulkReplace;
 
 export interface IExtHostTestItemApi {
-	children: Map<string, TestItemImpl>;
-	bus: Emitter<ExtHostTestItemEvent>;
+	parent?: TestItemImpl;
+	listener?: (evt: ExtHostTestItemEvent) => void;
 }
 
 const eventPrivateApis = new WeakMap<TestItemImpl, IExtHostTestItemApi>();
@@ -35,9 +59,216 @@ const eventPrivateApis = new WeakMap<TestItemImpl, IExtHostTestItemApi>();
 export const getPrivateApiFor = (impl: TestItemImpl) => {
 	let api = eventPrivateApis.get(impl);
 	if (!api) {
-		api = { children: new Map(), bus: new Emitter() };
+		api = {};
 		eventPrivateApis.set(impl, api);
 	}
 
 	return api;
 };
+
+const testItemPropAccessor = <K extends keyof vscode.TestItem>(
+	api: IExtHostTestItemApi,
+	key: K,
+	defaultValue: vscode.TestItem[K],
+	equals: (a: vscode.TestItem[K], b: vscode.TestItem[K]) => boolean
+) => {
+	let value = defaultValue;
+	return {
+		enumerable: true,
+		configurable: false,
+		get() {
+			return value;
+		},
+		set(newValue: vscode.TestItem[K]) {
+			if (!equals(value, newValue)) {
+				value = newValue;
+				api.listener?.({ op: ExtHostTestItemEventOp.SetProp, key, value: newValue });
+			}
+		},
+	};
+};
+
+type WritableProps = Pick<vscode.TestItem, 'range' | 'label' | 'description' | 'canResolveChildren' | 'busy' | 'error'>;
+
+const strictEqualComparator = <T>(a: T, b: T) => a === b;
+
+const propComparators: { [K in keyof Required<WritableProps>]: (a: vscode.TestItem[K], b: vscode.TestItem[K]) => boolean } = {
+	range: (a, b) => {
+		if (a === b) { return true; }
+		if (!a || !b) { return false; }
+		return a.isEqual(b);
+	},
+	label: strictEqualComparator,
+	description: strictEqualComparator,
+	busy: strictEqualComparator,
+	error: strictEqualComparator,
+	canResolveChildren: strictEqualComparator
+};
+
+const writablePropKeys = Object.keys(propComparators) as (keyof Required<WritableProps>)[];
+
+const makePropDescriptors = (api: IExtHostTestItemApi, label: string): { [K in keyof Required<WritableProps>]: PropertyDescriptor } => ({
+	range: testItemPropAccessor(api, 'range', undefined, propComparators.range),
+	label: testItemPropAccessor(api, 'label', label, propComparators.label),
+	description: testItemPropAccessor(api, 'description', undefined, propComparators.description),
+	canResolveChildren: testItemPropAccessor(api, 'canResolveChildren', false, propComparators.canResolveChildren),
+	busy: testItemPropAccessor(api, 'busy', false, propComparators.busy),
+	error: testItemPropAccessor(api, 'error', undefined, propComparators.error),
+});
+
+/**
+ * Returns a partial test item containing the writable properties in B that
+ * are different from A.
+ */
+export const diffTestItems = (a: vscode.TestItem, b: vscode.TestItem) => {
+	const output = new Map<keyof WritableProps, unknown>();
+	for (const key of writablePropKeys) {
+		const cmp = propComparators[key] as (a: unknown, b: unknown) => boolean;
+		if (!cmp(a[key], b[key])) {
+			output.set(key, b[key]);
+		}
+	}
+
+	return output;
+};
+
+export class DuplicateTestItemError extends Error {
+	constructor(id: string) {
+		super(`Attempted to insert a duplicate test item ID ${id}`);
+	}
+}
+
+export class InvalidTestItemError extends Error {
+	constructor(id: string) {
+		super(`TestItem with ID "${id}" is invalid. Make sure to create it from the createTestItem method.`);
+	}
+}
+
+export const createTestItemCollection = (owningItem: TestItemImpl):
+	vscode.TestItemCollection & { toJSON(): readonly vscode.TestItem[] } => {
+	const api = getPrivateApiFor(owningItem);
+	let all: readonly TestItemImpl[] | undefined;
+	let mapped = new Map<string, TestItemImpl>();
+
+	return {
+		/** @inheritdoc */
+		get all() {
+			if (!all) {
+				all = Object.freeze([...mapped.values()]);
+			}
+
+			return all;
+		},
+
+		/** @inheritdoc */
+		set all(items: readonly vscode.TestItem[]) {
+			const newMapped = new Map<string, TestItemImpl>();
+			const toDelete = new Set(mapped.keys());
+			const bulk: ITestItemBulkReplace = { op: ExtHostTestItemEventOp.Bulk, ops: [] };
+
+			for (const item of items) {
+				if (!(item instanceof TestItemImpl)) {
+					throw new InvalidTestItemError(item.id);
+				}
+
+				if (newMapped.has(item.id)) {
+					throw new DuplicateTestItemError(item.id);
+				}
+
+				newMapped.set(item.id, item);
+				toDelete.delete(item.id);
+				bulk.ops.push({ op: ExtHostTestItemEventOp.Upsert, item });
+			}
+
+			for (const id of toDelete.keys()) {
+				bulk.ops.push({ op: ExtHostTestItemEventOp.RemoveChild, id });
+			}
+
+			api.listener?.(bulk);
+
+			// important mutations come after firing, so if an error happens no
+			// changes will be "saved":
+			mapped = newMapped;
+			all = undefined;
+		},
+
+
+		/** @inheritdoc */
+		add(item: vscode.TestItem) {
+			if (!(item instanceof TestItemImpl)) {
+				throw new InvalidTestItemError(item.id);
+			}
+
+			mapped.set(item.id, item);
+			all = undefined;
+			api.listener?.({ op: ExtHostTestItemEventOp.Upsert, item });
+		},
+
+		/** @inheritdoc */
+		remove(id: string) {
+			if (mapped.delete(id)) {
+				all = undefined;
+				api.listener?.({ op: ExtHostTestItemEventOp.RemoveChild, id });
+			}
+		},
+
+		/** @inheritdoc */
+		get(itemId: string) {
+			return mapped.get(itemId);
+		},
+
+		/** JSON serialization function. */
+		toJSON() {
+			return this.all;
+		},
+	};
+};
+
+export class TestItemImpl implements vscode.TestItem {
+	public readonly id!: string;
+	public readonly uri!: vscode.Uri | undefined;
+	public readonly children!: vscode.TestItemCollection;
+	public readonly parent!: TestItemImpl | undefined;
+
+	public range!: vscode.Range | undefined;
+	public description!: string | undefined;
+	public label!: string;
+	public error!: string | vscode.MarkdownString;
+	public busy!: boolean;
+	public canResolveChildren!: boolean;
+
+	/**
+	 * Note that data is deprecated and here for back-compat only
+	 */
+	constructor(id: string, label: string, uri: vscode.Uri | undefined) {
+		const api = getPrivateApiFor(this);
+
+		Object.defineProperties(this, {
+			id: {
+				value: id,
+				enumerable: true,
+				writable: false,
+			},
+			uri: {
+				value: uri,
+				enumerable: true,
+				writable: false,
+			},
+			parent: {
+				enumerable: false,
+				get() { return api.parent; },
+			},
+			children: {
+				value: createTestItemCollection(this),
+				enumerable: true,
+				writable: false,
+			},
+			...makePropDescriptors(api, label),
+		});
+	}
+
+	/** @deprecated back compat */
+	public invalidateResults() {
+		getPrivateApiFor(this).listener?.({ op: ExtHostTestItemEventOp.Invalidated });
+	}
+}

src/vs/workbench/api/common/extHostTypeConverters.ts

@@ -26,6 +26,7 @@ import * as extHostProtocol from 'vs/workbench/api/common/extHost.protocol';
 import { CommandsConverter } from 'vs/workbench/api/common/extHostCommands';
 import { ExtHostDocumentsAndEditors } from 'vs/workbench/api/common/extHostDocumentsAndEditors';
 import { ExtHostNotebookController } from 'vs/workbench/api/common/extHostNotebook';
+import { getPrivateApiFor, TestItemImpl } from 'vs/workbench/api/common/extHostTestingPrivateApi';
 import { SaveReason } from 'vs/workbench/common/editor';
 import * as notebooks from 'vs/workbench/contrib/notebook/common/notebookCommon';
 import { ICellRange } from 'vs/workbench/contrib/notebook/common/notebookRange';
@@ -1665,7 +1666,6 @@ export namespace TestItem {
 			label: item.label,
 			uri: URI.revive(item.uri),
 			range: Range.to(item.range || undefined),
-			dispose: () => undefined,
 			invalidateResults: () => undefined,
 			canResolveChildren: false,
 			busy: false,
@@ -1673,17 +1673,19 @@ export namespace TestItem {
 		};
 	}
 
-	export function to(item: ITestItem, parent?: vscode.TestItem): types.TestItemImpl {
-		const testItem = new types.TestItemImpl(item.extId, item.label, URI.revive(item.uri), undefined, parent);
+	export function to(item: ITestItem): TestItemImpl {
+		const testItem = new TestItemImpl(item.extId, item.label, URI.revive(item.uri));
 		testItem.range = Range.to(item.range || undefined);
 		testItem.description = item.description || undefined;
 		return testItem;
 	}
 
-	export function toItemFromContext(context: ITestItemContext): types.TestItemImpl {
-		let node: types.TestItemImpl | undefined;
+	export function toItemFromContext(context: ITestItemContext): TestItemImpl {
+		let node: TestItemImpl | undefined;
 		for (const test of context.tests) {
-			node = to(test.item, node);
+			const next = to(test.item);
+			getPrivateApiFor(next).parent = node;
+			node = next;
 		}
 
 		return node!;

src/vs/workbench/api/common/extHostTypes.ts

@@ -7,14 +7,13 @@ import { asArray, coalesceInPlace, equals } from 'vs/base/common/arrays';
 import { illegalArgument } from 'vs/base/common/errors';
 import { IRelativePattern } from 'vs/base/common/glob';
 import { MarkdownString as BaseMarkdownString } from 'vs/base/common/htmlContent';
-import { ReadonlyMapView, ResourceMap } from 'vs/base/common/map';
+import { ResourceMap } from 'vs/base/common/map';
 import { Mimes, normalizeMimeType } from 'vs/base/common/mime';
 import { isArray, isStringArray } from 'vs/base/common/types';
 import { URI } from 'vs/base/common/uri';
 import { generateUuid } from 'vs/base/common/uuid';
 import { FileSystemProviderErrorCode, markAsFileSystemProviderError } from 'vs/platform/files/common/files';
 import { RemoteAuthorityResolverErrorCode } from 'vs/platform/remote/common/remoteAuthorityResolver';
-import { getPrivateApiFor, ExtHostTestItemEventType, IExtHostTestItemApi } from 'vs/workbench/api/common/extHostTestingPrivateApi';
 import { CellEditType, ICellPartialMetadataEdit, IDocumentMetadataEdit } from 'vs/workbench/contrib/notebook/common/notebookCommon';
 import type * as vscode from 'vscode';
 
@@ -3302,130 +3301,21 @@ export enum TestMessageSeverity {
 	Hint = 3
 }
 
-const testItemPropAccessor = <K extends keyof vscode.TestItem>(
-	api: IExtHostTestItemApi,
-	key: K,
-	defaultValue: vscode.TestItem[K],
-	equals: (a: vscode.TestItem[K], b: vscode.TestItem[K]) => boolean
-) => {
-	let value = defaultValue;
-	return {
-		enumerable: true,
-		configurable: false,
-		get() {
-			return value;
-		},
-		set(newValue: vscode.TestItem[K]) {
-			if (!equals(value, newValue)) {
-				value = newValue;
-				api.bus.fire([ExtHostTestItemEventType.SetProp, key, newValue]);
-			}
-		},
-	};
-};
-
-const strictEqualComparator = <T>(a: T, b: T) => a === b;
-const rangeComparator = (a: vscode.Range | undefined, b: vscode.Range | undefined) => {
-	if (a === b) { return true; }
-	if (!a || !b) { return false; }
-	return a.isEqual(b);
-};
-
 export enum TestRunConfigurationGroup {
 	Run = 1,
 	Debug = 2,
 	Coverage = 3,
 }
 
+@es5ClassCompat
 export class TestRunRequest implements vscode.TestRunRequest {
 	constructor(
-		public readonly tests: vscode.TestItem[],
+		public readonly include?: vscode.TestItem[],
 		public readonly exclude?: vscode.TestItem[] | undefined,
 		public readonly configuration?: vscode.TestRunConfiguration,
 	) { }
 }
 
-export class TestItemImpl implements vscode.TestItem {
-	public readonly id!: string;
-	public readonly uri!: vscode.Uri | undefined;
-	public readonly children!: ReadonlyMap<string, TestItemImpl>;
-	public readonly parent!: TestItemImpl | undefined;
-
-	public range!: vscode.Range | undefined;
-	public description!: string | undefined;
-	public label!: string;
-	public error!: string | vscode.MarkdownString;
-	public busy!: boolean;
-	public canResolveChildren!: boolean;
-
-	/**
-	 * Note that data is deprecated and here for back-compat only
-	 */
-	constructor(id: string, label: string, uri: vscode.Uri | undefined, public data: any, parent: vscode.TestItem | undefined) {
-		const api = getPrivateApiFor(this);
-
-		Object.defineProperties(this, {
-			id: {
-				value: id,
-				enumerable: true,
-				writable: false,
-			},
-			uri: {
-				value: uri,
-				enumerable: true,
-				writable: false,
-			},
-			parent: {
-				enumerable: false,
-				value: parent,
-				writable: false,
-			},
-			children: {
-				value: new ReadonlyMapView(api.children),
-				enumerable: true,
-				writable: false,
-			},
-			range: testItemPropAccessor(api, 'range', undefined, rangeComparator),
-			label: testItemPropAccessor(api, 'label', label, strictEqualComparator),
-			description: testItemPropAccessor(api, 'description', undefined, strictEqualComparator),
-			canResolveChildren: testItemPropAccessor(api, 'canResolveChildren', false, strictEqualComparator),
-			busy: testItemPropAccessor(api, 'busy', false, strictEqualComparator),
-			error: testItemPropAccessor(api, 'error', undefined, strictEqualComparator),
-		});
-
-		if (parent) {
-			if (!(parent instanceof TestItemImpl)) {
-				throw new Error(`The "parent" passed in for TestItem ${id} is invalid`);
-			}
-
-			const parentApi = getPrivateApiFor(parent);
-			if (parentApi.children.has(id)) {
-				throw new Error(`Attempted to insert a duplicate test item ID ${id}`);
-			}
-
-			parentApi.children.set(id, this);
-			parentApi.bus.fire([ExtHostTestItemEventType.NewChild, this]);
-		}
-	}
-
-	/** @deprecated back compat */
-	public invalidate() {
-		return this.invalidateResults();
-	}
-
-	public invalidateResults() {
-		getPrivateApiFor(this).bus.fire([ExtHostTestItemEventType.Invalidated]);
-	}
-
-	public dispose() {
-		if (this.parent) {
-			getPrivateApiFor(this.parent).children.delete(this.id);
-		}
-
-		getPrivateApiFor(this).bus.fire([ExtHostTestItemEventType.Disposed]);
-	}
-}
-
 @es5ClassCompat
 export class TestMessage implements vscode.TestMessage {
 	public severity = TestMessageSeverity.Error;

src/vs/workbench/contrib/testing/browser/icons.ts

@@ -14,8 +14,8 @@ export const testingViewIcon = registerIcon('test-view-icon', Codicon.beaker, lo
 export const testingRunIcon = registerIcon('testing-run-icon', Codicon.run, localize('testingRunIcon', 'Icon of the "run test" action.'));
 export const testingRunAllIcon = registerIcon('testing-run-all-icon', Codicon.runAll, localize('testingRunAllIcon', 'Icon of the "run all tests" action.'));
 // todo: https://github.com/microsoft/vscode-codicons/issues/72
-export const testingDebugAllIcon = registerIcon('testing-debug-all-icon', Codicon.debugAlt, localize('testingDebugAllIcon', 'Icon of the "debug all tests" action.'));
-export const testingDebugIcon = registerIcon('testing-debug-icon', Codicon.debugAlt, localize('testingDebugIcon', 'Icon of the "debug test" action.'));
+export const testingDebugAllIcon = registerIcon('testing-debug-all-icon', Codicon.debugAltSmall, localize('testingDebugAllIcon', 'Icon of the "debug all tests" action.'));
+export const testingDebugIcon = registerIcon('testing-debug-icon', Codicon.debugAltSmall, localize('testingDebugIcon', 'Icon of the "debug test" action.'));
 export const testingCancelIcon = registerIcon('testing-cancel-icon', Codicon.debugStop, localize('testingCancelIcon', 'Icon to cancel ongoing test runs.'));
 export const testingFilterIcon = registerIcon('testing-filter', Codicon.filter, localize('filterIcon', 'Icon for the \'Filter\' action in the testing view.'));
 export const testingAutorunIcon = registerIcon('testing-autorun', Codicon.debugRerun, localize('autoRunIcon', 'Icon for the \'Autorun\' toggle in the testing view.'));

src/vs/workbench/contrib/testing/common/ownedTestCollection.ts

@@ -6,13 +6,11 @@
 import { Barrier, isThenable, RunOnceScheduler } from 'vs/base/common/async';
 import { CancellationToken } from 'vs/base/common/cancellation';
 import { Emitter } from 'vs/base/common/event';
-import { Iterable } from 'vs/base/common/iterator';
 import { Disposable } from 'vs/base/common/lifecycle';
 import { assertNever } from 'vs/base/common/types';
-import { ExtHostTestItemEvent, ExtHostTestItemEventType, getPrivateApiFor } from 'vs/workbench/api/common/extHostTestingPrivateApi';
+import { diffTestItems, ExtHostTestItemEvent, ExtHostTestItemEventOp, getPrivateApiFor, TestItemImpl } from 'vs/workbench/api/common/extHostTestingPrivateApi';
 import * as Convert from 'vs/workbench/api/common/extHostTypeConverters';
-import { TestItemImpl } from 'vs/workbench/api/common/extHostTypes';
-import { applyTestItemUpdate, InternalTestItem, TestDiffOpType, TestItemExpandState, TestsDiff, TestsDiffOp } from 'vs/workbench/contrib/testing/common/testCollection';
+import { applyTestItemUpdate, TestDiffOpType, TestItemExpandState, TestsDiff, TestsDiffOp } from 'vs/workbench/contrib/testing/common/testCollection';
 
 type TestItemRaw = Convert.TestItem.Raw;
 
@@ -23,7 +21,9 @@ export interface IHierarchyProvider {
 /**
  * @private
  */
-export interface OwnedCollectionTestItem extends InternalTestItem {
+export interface OwnedCollectionTestItem {
+	expand: TestItemExpandState;
+	parent: string | null;
 	actual: TestItemImpl;
 	/**
 	 * Number of levels of items below this one that are expanded. May be infinite.
@@ -52,7 +52,7 @@ export const enum TestPosition {
  * for test trees. Internally it indexes tests by their extension ID in
  * a map.
  */
-export class TestTree<T extends InternalTestItem> {
+export class TestTree<T extends OwnedCollectionTestItem> {
 	private readonly map = new Map<string, T>();
 	private readonly _roots = new Set<T>();
 	public readonly roots: ReadonlySet<T> = this._roots;
@@ -69,11 +69,11 @@ export class TestTree<T extends InternalTestItem> {
 	 * @throws if a duplicate item is inserted
 	 */
 	public add(test: T) {
-		if (this.map.has(test.item.extId)) {
-			throw new Error(`Attempted to insert a duplicate test item ID ${test.item.extId}`);
+		if (this.map.has(test.actual.id)) {
+			throw new Error(`Attempted to insert a duplicate test item ID ${test.actual.id}`);
 		}
 
-		this.map.set(test.item.extId, test);
+		this.map.set(test.actual.id, test);
 		if (!test.parent) {
 			this._roots.add(test);
 		}
@@ -150,12 +150,11 @@ export class TestTree<T extends InternalTestItem> {
  * @private
  */
 export class SingleUseTestCollection extends Disposable {
-	protected readonly testItemToInternal = new Map<TestItemRaw, OwnedCollectionTestItem>();
 	private readonly debounceSendDiff = this._register(new RunOnceScheduler(() => this.flushDiff(), 200));
 	private readonly diffOpEmitter = this._register(new Emitter<TestsDiff>());
 	private _resolveHandler?: (item: TestItemRaw) => Promise<void> | void;
 
-	public readonly root = new TestItemImpl(`${this.controllerId}Root`, this.controllerId, undefined, undefined, undefined);
+	public readonly root = new TestItemImpl(`${this.controllerId}Root`, this.controllerId, undefined);
 	public readonly tree = new TestTree<OwnedCollectionTestItem>();
 	protected diff: TestsDiff = [];
 
@@ -163,7 +162,7 @@ export class SingleUseTestCollection extends Disposable {
 		private readonly controllerId: string,
 	) {
 		super();
-		this.addItemInner(this.root, null);
+		this.upsertItem(this.root, null);
 	}
 
 	/**
@@ -171,7 +170,7 @@ export class SingleUseTestCollection extends Disposable {
 	 */
 	public set resolveHandler(handler: undefined | ((item: TestItemRaw) => void)) {
 		this._resolveHandler = handler;
-		for (const test of this.testItemToInternal.values()) {
+		for (const test of this.tree) {
 			this.updateExpandability(test);
 		}
 	}
@@ -181,18 +180,6 @@ export class SingleUseTestCollection extends Disposable {
 	 */
 	public readonly onDidGenerateDiff = this.diffOpEmitter.event;
 
-	public get roots() {
-		return Iterable.filter(this.testItemToInternal.values(), t => t.parent === null);
-	}
-
-	/**
-	 * Gets test information by its reference, if it was defined and still exists
-	 * in this extension host.
-	 */
-	public getTestByReference(item: TestItemRaw) {
-		return this.testItemToInternal.get(item);
-	}
-
 	/**
 	 * Gets a diff of all changes that have been made, and clears the diff queue.
 	 */
@@ -257,8 +244,8 @@ export class SingleUseTestCollection extends Disposable {
 	}
 
 	public override dispose() {
-		for (const item of this.testItemToInternal.values()) {
-			getPrivateApiFor(item.actual).bus.dispose();
+		for (const item of this.tree) {
+			getPrivateApiFor(item.actual).listener = undefined;
 		}
 
 		this.diff = [];
@@ -268,21 +255,27 @@ export class SingleUseTestCollection extends Disposable {
 	private onTestItemEvent(internal: OwnedCollectionTestItem, evt: ExtHostTestItemEvent) {
 		const extId = internal?.actual.id;
 
-		switch (evt[0]) {
-			case ExtHostTestItemEventType.Invalidated:
+		switch (evt.op) {
+			case ExtHostTestItemEventOp.Invalidated:
 				this.pushDiff([TestDiffOpType.Retire, extId]);
 				break;
 
-			case ExtHostTestItemEventType.Disposed:
-				this.removeItem(internal);
+			case ExtHostTestItemEventOp.RemoveChild:
+				this.removeItem(evt.id);
 				break;
 
-			case ExtHostTestItemEventType.NewChild:
-				this.addItemInner(evt[1], internal);
+			case ExtHostTestItemEventOp.Upsert:
+				this.upsertItem(evt.item, internal);
 				break;
 
-			case ExtHostTestItemEventType.SetProp:
-				const [_, key, value] = evt;
+			case ExtHostTestItemEventOp.Bulk:
+				for (const op of evt.ops) {
+					this.onTestItemEvent(internal, op);
+				}
+				break;
+
+			case ExtHostTestItemEventOp.SetProp:
+				const { key, value } = evt;
 				switch (key) {
 					case 'canResolveChildren':
 						this.updateExpandability(internal);
@@ -299,54 +292,88 @@ export class SingleUseTestCollection extends Disposable {
 				}
 				break;
 			default:
-				assertNever(evt[0]);
+				assertNever(evt);
 		}
 	}
 
-	private addItemInner(actual: TestItemRaw, parent: OwnedCollectionTestItem | null) {
+	private upsertItem(actual: TestItemRaw, parent: OwnedCollectionTestItem | null) {
 		if (!(actual instanceof TestItemImpl)) {
 			throw new Error(`TestItems provided to the VS Code API must extend \`vscode.TestItem\`, but ${actual.id} did not`);
 		}
 
-		if (this.testItemToInternal.has(actual)) {
-			throw new Error(`Attempted to add a single TestItem ${actual.id} multiple times to the tree`);
+
+		// If the item already exists under a different parent, remove it.
+		let internal = this.tree.get(actual.id);
+		if (internal && internal.parent !== parent?.actual.id) {
+			(internal.actual.parent ?? this.root).children.remove(actual.id);
+			internal = undefined;
+		}
+
+		// Case 1: a brand new item
+		if (!internal) {
+			const parentId = parent ? parent.actual.id : null;
+			// always expand root node to know if there are tests (and whether to show the welcome view)
+			const pExpandLvls = parent ? parent.expandLevels : 1;
+			internal = {
+				actual,
+				parent: parentId,
+				expandLevels: pExpandLvls /* intentionally undefined or 0 */ ? pExpandLvls - 1 : undefined,
+				expand: TestItemExpandState.NotExpandable, // updated by `connectItemAndChildren`
+			};
+
+			this.tree.add(internal);
+			this.pushDiff([
+				TestDiffOpType.Add,
+				{ parent: parentId, controllerId: this.controllerId, expand: internal.expand, item: Convert.TestItem.from(actual) },
+			]);
+
+			this.connectItemAndChildren(actual, internal, parent);
+			return;
+		}
+
+		// Case 2: re-insertion of an existing item, no-op
+		if (internal.actual === actual) {
+			this.connectItem(actual, internal, parent); // re-connect in case the parent changed
+			return; // no-op
 		}
 
-		if (this.tree.has(actual.id)) {
-			throw new Error(`Attempted to insert a duplicate test item ID ${actual.id}`);
+		// Case 3: upsert of an existing item by ID, with a new instance
+		const oldChildren = internal.actual.children.all;
+		const oldActual = internal.actual;
+		const changedProps = diffTestItems(oldActual, actual);
+		getPrivateApiFor(oldActual).listener = undefined;
+
+		internal.actual = actual;
+		internal.expand = TestItemExpandState.NotExpandable; // updated by `connectItemAndChildren`
+		for (const [key, value] of changedProps) {
+			this.onTestItemEvent(internal, { op: ExtHostTestItemEventOp.SetProp, key, value });
 		}
 
-		const parentId = parent ? parent.item.extId : null;
-		// always expand root node to know if there are tests (and whether to show the welcome view)
-		const pExpandLvls = parent ? parent.expandLevels : 1;
-		const internal: OwnedCollectionTestItem = {
-			actual,
-			parent: parentId,
-			item: Convert.TestItem.from(actual),
-			expandLevels: pExpandLvls /* intentionally undefined or 0 */ ? pExpandLvls - 1 : undefined,
-			expand: TestItemExpandState.NotExpandable, // updated by `updateExpandability` down below
-			controllerId: this.controllerId,
-		};
+		this.connectItemAndChildren(actual, internal, parent);
 
-		this.tree.add(internal);
-		this.testItemToInternal.set(actual, internal);
-		this.pushDiff([
-			TestDiffOpType.Add,
-			{ parent: parentId, controllerId: this.controllerId, expand: internal.expand, item: internal.item },
-		]);
+		// Remove any children still referencing the old parent that aren't
+		// included in the new one. Note that children might have moved to a new
+		// parent, so the parent ID check is done.
+		for (const child of oldChildren) {
+			if (!actual.children.get(child.id) && this.tree.get(child.id)?.parent === actual.id) {
+				this.removeItem(child.id);
+			}
+		}
+	}
 
+	private connectItem(actual: TestItemImpl, internal: OwnedCollectionTestItem, parent: OwnedCollectionTestItem | null) {
 		const api = getPrivateApiFor(actual);
-		api.bus.event(this.onTestItemEvent.bind(this, internal));
-
-		// important that this comes after binding the event bus otherwise we
-		// might miss a synchronous discovery completion
+		api.parent = parent && parent.actual !== this.root ? parent.actual : undefined;
+		api.listener = evt => this.onTestItemEvent(internal, evt);
 		this.updateExpandability(internal);
+	}
+
+	private connectItemAndChildren(actual: TestItemImpl, internal: OwnedCollectionTestItem, parent: OwnedCollectionTestItem | null) {
+		this.connectItem(actual, internal, parent);
 
 		// Discover any existing children that might have already been added
-		for (const child of api.children.values()) {
-			if (!this.testItemToInternal.has(child)) {
-				this.addItemInner(child, internal);
-			}
+		for (const child of actual.children.all) {
+			this.upsertItem(child, internal);
 		}
 	}
 
@@ -391,7 +418,7 @@ export class SingleUseTestCollection extends Disposable {
 			return;
 		}
 
-		const asyncChildren = [...internal.actual.children.values()]
+		const asyncChildren = internal.actual.children.all
 			.map(c => this.expand(c.id, levels))
 			.filter(isThenable);
 
@@ -443,19 +470,24 @@ export class SingleUseTestCollection extends Disposable {
 		this.pushDiff([TestDiffOpType.Update, { extId: internal.actual.id, expand: internal.expand }]);
 	}
 
-	private removeItem(internal: OwnedCollectionTestItem) {
-		this.pushDiff([TestDiffOpType.Remove, internal.actual.id]);
+	private removeItem(childId: string) {
+		const childItem = this.tree.get(childId);
+		if (!childItem) {
+			throw new Error('attempting to remove non-existent child');
+		}
+
+		this.pushDiff([TestDiffOpType.Remove, childId]);
 
-		const queue: (OwnedCollectionTestItem | undefined)[] = [internal];
+		const queue: (OwnedCollectionTestItem | undefined)[] = [childItem];
 		while (queue.length) {
 			const item = queue.pop();
 			if (!item) {
 				continue;
 			}
 
-			this.tree.delete(item.item.extId);
-			this.testItemToInternal.delete(item.actual);
-			for (const child of item.actual.children.values()) {
+			getPrivateApiFor(item.actual).listener = undefined;
+			this.tree.delete(item.actual.id);
+			for (const child of item.actual.children.all) {
 				queue.push(this.tree.get(child.id));
 			}
 		}

src/vs/workbench/contrib/testing/common/testCollection.ts

@@ -10,6 +10,8 @@ import { IPosition } from 'vs/editor/common/core/position';
 import { IRange, Range } from 'vs/editor/common/core/range';
 import { TestMessageSeverity, TestResultState } from 'vs/workbench/api/common/extHostTypes';
 
+export { TestResultState } from 'vs/workbench/api/common/extHostTypes';
+
 export interface ITestIdWithSrc {
 	testId: string;
 	controllerId: string;
@@ -74,7 +76,7 @@ export interface ResolvedTestRunRequest {
  */
 export interface ExtensionRunTestsRequest {
 	id: string;
-	tests: string[];
+	include: string[];
 	exclude: string[];
 	controllerId: string;
 	config?: { group: TestRunConfigurationBitset, id: number };

src/vs/workbench/contrib/testing/common/testResultService.ts

@@ -156,7 +156,7 @@ export class TestResultService implements ITestResultService {
 				profileGroup: config.group,
 				profileId: config.profileId,
 				controllerId: req.controllerId,
-				testIds: req.tests,
+				testIds: req.include,
 			});
 		}
 

src/vs/workbench/contrib/testing/common/testStubs.ts

@@ -4,12 +4,12 @@
  *--------------------------------------------------------------------------------------------*/
 
 import { URI } from 'vs/base/common/uri';
-import { TestItemImpl, TestResultState } from 'vs/workbench/api/common/extHostTypes';
+import { TestItemImpl } from 'vs/workbench/api/common/extHostTestingPrivateApi';
 import { MainThreadTestCollection } from 'vs/workbench/contrib/testing/common/mainThreadTestCollection';
 import { TestSingleUseCollection } from 'vs/workbench/contrib/testing/test/common/ownedTestCollection';
 
 export * as Convert from 'vs/workbench/api/common/extHostTypeConverters';
-export { TestItemImpl, TestResultState } from 'vs/workbench/api/common/extHostTypes';
+export { TestItemImpl } from 'vs/workbench/api/common/extHostTestingPrivateApi';
 
 /**
  * Gets a main thread test collection initialized with the given set of
@@ -29,17 +29,18 @@ export const testStubs = {
 		collection.root.canResolveChildren = true;
 		collection.resolveHandler = item => {
 			if (item === collection.root) {
-				const a = new TestItemImpl(idPrefix + 'a', 'a', URI.file('/'), undefined, collection.root);
+				const a = new TestItemImpl(idPrefix + 'a', 'a', URI.file('/'));
 				a.canResolveChildren = true;
-				new TestItemImpl(idPrefix + 'b', 'b', URI.file('/'), undefined, collection.root);
+				const b = new TestItemImpl(idPrefix + 'b', 'b', URI.file('/'));
+				item.children.all = [a, b];
 			} else if (item.id === idPrefix + 'a') {
-				new TestItemImpl(idPrefix + 'aa', 'aa', URI.file('/'), undefined, item);
-				new TestItemImpl(idPrefix + 'ab', 'ab', URI.file('/'), undefined, item);
+				item.children.all = [
+					new TestItemImpl(idPrefix + 'aa', 'aa', URI.file('/')),
+					new TestItemImpl(idPrefix + 'ab', 'ab', URI.file('/')),
+				];
 			}
 		};
 
 		return collection;
 	},
 };
-
-export const ReExportedTestRunState = TestResultState;

src/vs/workbench/contrib/testing/common/testingStates.ts

@@ -5,6 +5,8 @@
 
 import { TestResultState } from 'vs/workbench/api/common/extHostTypes';
 
+export { TestResultState } from 'vs/workbench/api/common/extHostTypes';
+
 export type TreeStateNode = { statusNode: true; state: TestResultState; priority: number };
 
 /**

src/vs/workbench/contrib/testing/test/browser/explorerProjections/hierarchalByLocation.test.ts

@@ -7,8 +7,9 @@ import * as assert from 'assert';
 import { Emitter } from 'vs/base/common/event';
 import { HierarchicalByLocationProjection } from 'vs/workbench/contrib/testing/browser/explorerProjections/hierarchalByLocation';
 import { TestDiffOpType, TestItemExpandState, TestResultItem } from 'vs/workbench/contrib/testing/common/testCollection';
+import { TestResultState } from 'vs/workbench/contrib/testing/common/testingStates';
 import { TestResultItemChange, TestResultItemChangeReason } from 'vs/workbench/contrib/testing/common/testResult';
-import { Convert, TestItemImpl, TestResultState } from 'vs/workbench/contrib/testing/common/testStubs';
+import { Convert, TestItemImpl } from 'vs/workbench/contrib/testing/common/testStubs';
 import { TestTreeTestHarness } from 'vs/workbench/contrib/testing/test/browser/testObjectTree';
 
 class TestHierarchicalByLocationProjection extends HierarchicalByLocationProjection {
@@ -53,10 +54,10 @@ suite('Workbench - Testing Explorer Hierarchal by Location Projection', () => {
 		harness.flush();
 		harness.pushDiff([
 			TestDiffOpType.Add,
-			{ controllerId: 'ctrl2', parent: null, expand: TestItemExpandState.Expanded, item: Convert.TestItem.from(new TestItemImpl('c', 'c', undefined, undefined, undefined)) },
+			{ controllerId: 'ctrl2', parent: null, expand: TestItemExpandState.Expanded, item: Convert.TestItem.from(new TestItemImpl('c', 'c', undefined)) },
 		], [
 			TestDiffOpType.Add,
-			{ controllerId: 'ctrl2', parent: 'c', expand: TestItemExpandState.NotExpandable, item: Convert.TestItem.from(new TestItemImpl('c-a', 'ca', undefined, undefined, undefined)) },
+			{ controllerId: 'ctrl2', parent: 'c', expand: TestItemExpandState.NotExpandable, item: Convert.TestItem.from(new TestItemImpl('c-a', 'ca', undefined)) },
 		]);
 
 		assert.deepStrictEqual(harness.flush(), [
@@ -74,7 +75,7 @@ suite('Workbench - Testing Explorer Hierarchal by Location Projection', () => {
 			{ e: 'b' }
 		]);
 
-		new TestItemImpl('ac', 'ac', undefined, undefined, harness.c.root.children.get('id-a')!);
+		harness.c.root.children.get('id-a')!.children.add(new TestItemImpl('ac', 'ac', undefined));
 
 		assert.deepStrictEqual(harness.flush(), [
 			{ e: 'a', children: [{ e: 'aa' }, { e: 'ab' }, { e: 'ac' }] },
@@ -91,7 +92,7 @@ suite('Workbench - Testing Explorer Hierarchal by Location Projection', () => {
 			{ e: 'b' }
 		]);
 
-		harness.c.root.children.get('id-a')!.children.get('id-ab')!.dispose();
+		harness.c.root.children.get('id-a')!.children.remove('id-ab');
 
 		assert.deepStrictEqual(harness.flush(), [
 			{ e: 'a', children: [{ e: 'aa' }] },
@@ -104,7 +105,7 @@ suite('Workbench - Testing Explorer Hierarchal by Location Projection', () => {
 		resultsService.getStateById = () => [undefined, resultInState(TestResultState.Failed)];
 
 		const resultInState = (state: TestResultState): TestResultItem => ({
-			item: harness.c.itemToInternal.get(harness.c.root.children.get('id-a')!)!.item,
+			item: Convert.TestItem.from(harness.c.tree.get('id-a')!.actual),
 			parent: 'id-root',
 			tasks: [],
 			retired: false,

src/vs/workbench/contrib/testing/test/browser/explorerProjections/hierarchalByName.test.ts

@@ -42,10 +42,10 @@ suite('Workbench - Testing Explorer Hierarchal by Name Projection', () => {
 		harness.flush();
 		harness.pushDiff([
 			TestDiffOpType.Add,
-			{ controllerId: 'ctrl2', parent: null, expand: TestItemExpandState.Expanded, item: Convert.TestItem.from(new TestItemImpl('c', 'root2', undefined, undefined, undefined)) },
+			{ controllerId: 'ctrl2', parent: null, expand: TestItemExpandState.Expanded, item: Convert.TestItem.from(new TestItemImpl('c', 'root2', undefined)) },
 		], [
 			TestDiffOpType.Add,
-			{ controllerId: 'ctrl2', parent: 'c', expand: TestItemExpandState.NotExpandable, item: Convert.TestItem.from(new TestItemImpl('c-a', 'c', undefined, undefined, undefined)) },
+			{ controllerId: 'ctrl2', parent: 'c', expand: TestItemExpandState.NotExpandable, item: Convert.TestItem.from(new TestItemImpl('c-a', 'c', undefined)) },
 		]);
 
 		assert.deepStrictEqual(harness.flush(), [
@@ -57,7 +57,7 @@ suite('Workbench - Testing Explorer Hierarchal by Name Projection', () => {
 	test('updates nodes if they add children', async () => {
 		harness.flush();
 
-		new TestItemImpl('ac', 'ac', undefined, undefined, harness.c.root.children.get('id-a')!);
+		harness.c.root.children.get('id-a')!.children.add(new TestItemImpl('ac', 'ac', undefined));
 
 		assert.deepStrictEqual(harness.flush(), [
 			{ e: 'aa' },
@@ -69,7 +69,7 @@ suite('Workbench - Testing Explorer Hierarchal by Name Projection', () => {
 
 	test('updates nodes if they remove children', async () => {
 		harness.flush();
-		harness.c.root.children.get('id-a')!.children.get('id-ab')!.dispose();
+		harness.c.root.children.get('id-a')!.children.remove('id-ab');
 
 		assert.deepStrictEqual(harness.flush(), [
 			{ e: 'aa' },
@@ -79,7 +79,7 @@ suite('Workbench - Testing Explorer Hierarchal by Name Projection', () => {
 
 	test('swaps when node is no longer leaf', async () => {
 		harness.flush();
-		new TestItemImpl('ba', 'ba', undefined, undefined, harness.c.root.children.get('id-b')!);
+		harness.c.root.children.get('id-b')!.children.add(new TestItemImpl('ba', 'ba', undefined));
 
 		assert.deepStrictEqual(harness.flush(), [
 			{ e: 'aa' },

src/vs/workbench/contrib/testing/test/common/ownedTestCollection.ts

@@ -7,10 +7,6 @@ import { SingleUseTestCollection } from 'vs/workbench/contrib/testing/common/own
 import { TestsDiff } from 'vs/workbench/contrib/testing/common/testCollection';
 
 export class TestSingleUseCollection extends SingleUseTestCollection {
-	public get itemToInternal() {
-		return this.testItemToInternal;
-	}
-
 	public get currentDiff() {
 		return this.diff;
 	}

src/vs/workbench/contrib/testing/test/common/testResultService.test.ts

@@ -12,10 +12,11 @@ import { NullLogService } from 'vs/platform/log/common/log';
 import { SingleUseTestCollection } from 'vs/workbench/contrib/testing/common/ownedTestCollection';
 import { ITestTaskState, ResolvedTestRunRequest, TestResultItem, TestRunConfigurationBitset } from 'vs/workbench/contrib/testing/common/testCollection';
 import { TestConfigurationService } from 'vs/workbench/contrib/testing/common/testConfigurationService';
+import { TestResultState } from 'vs/workbench/contrib/testing/common/testingStates';
 import { getPathForTestInResult, HydratedTestResult, LiveOutputController, LiveTestResult, makeEmptyCounts, resultItemParents, TestResultItemChange, TestResultItemChangeReason } from 'vs/workbench/contrib/testing/common/testResult';
 import { TestResultService } from 'vs/workbench/contrib/testing/common/testResultService';
 import { InMemoryResultStorage, ITestResultStorage } from 'vs/workbench/contrib/testing/common/testResultStorage';
-import { Convert, getInitializedMainTestCollection, ReExportedTestRunState as TestRunState, TestResultState, testStubs } from 'vs/workbench/contrib/testing/common/testStubs';
+import { Convert, getInitializedMainTestCollection, testStubs } from 'vs/workbench/contrib/testing/common/testStubs';
 import { TestStorageService } from 'vs/workbench/test/common/workbenchTestServices';
 
 export const emptyOutputController = () => new LiveOutputController(
@@ -100,29 +101,29 @@ suite('Workbench - Test Results Service', () => {
 		test('initializes with valid counts', () => {
 			assert.deepStrictEqual(r.counts, {
 				...makeEmptyCounts(),
-				[TestRunState.Queued]: 2,
-				[TestRunState.Unset]: 2,
+				[TestResultState.Queued]: 2,
+				[TestResultState.Unset]: 2,
 			});
 		});
 
 		test('setAllToState', () => {
 			changed.clear();
-			r.setAllToState(TestRunState.Queued, 't', (_, t) => t.item.label !== 'root');
+			r.setAllToState(TestResultState.Queued, 't', (_, t) => t.item.label !== 'root');
 			assert.deepStrictEqual(r.counts, {
 				...makeEmptyCounts(),
-				[TestRunState.Unset]: 1,
-				[TestRunState.Queued]: 3,
+				[TestResultState.Unset]: 1,
+				[TestResultState.Queued]: 3,
 			});
 
-			r.setAllToState(TestRunState.Failed, 't', (_, t) => t.item.label !== 'root');
+			r.setAllToState(TestResultState.Failed, 't', (_, t) => t.item.label !== 'root');
 			assert.deepStrictEqual(r.counts, {
 				...makeEmptyCounts(),
-				[TestRunState.Unset]: 1,
-				[TestRunState.Failed]: 3,
+				[TestResultState.Unset]: 1,
+				[TestResultState.Failed]: 3,
 			});
 
-			assert.deepStrictEqual(r.getStateById('id-a')?.ownComputedState, TestRunState.Failed);
-			assert.deepStrictEqual(r.getStateById('id-a')?.tasks[0].state, TestRunState.Failed);
+			assert.deepStrictEqual(r.getStateById('id-a')?.ownComputedState, TestResultState.Failed);
+			assert.deepStrictEqual(r.getStateById('id-a')?.tasks[0].state, TestResultState.Failed);
 			assert.deepStrictEqual(getChangeSummary(), [
 				{ label: 'a', reason: TestResultItemChangeReason.OwnStateChange },
 				{ label: 'aa', reason: TestResultItemChangeReason.OwnStateChange },
@@ -133,16 +134,16 @@ suite('Workbench - Test Results Service', () => {
 
 		test('updateState', () => {
 			changed.clear();
-			r.updateState('id-aa', 't', TestRunState.Running);
+			r.updateState('id-aa', 't', TestResultState.Running);
 			assert.deepStrictEqual(r.counts, {
 				...makeEmptyCounts(),
-				[TestRunState.Unset]: 2,
-				[TestRunState.Running]: 1,
-				[TestRunState.Queued]: 1,
+				[TestResultState.Unset]: 2,
+				[TestResultState.Running]: 1,
+				[TestResultState.Queued]: 1,
 			});
-			assert.deepStrictEqual(r.getStateById('id-aa')?.ownComputedState, TestRunState.Running);
+			assert.deepStrictEqual(r.getStateById('id-aa')?.ownComputedState, TestResultState.Running);
 			// update computed state:
-			assert.deepStrictEqual(r.getStateById(tests.root.id)?.computedState, TestRunState.Running);
+			assert.deepStrictEqual(r.getStateById(tests.root.id)?.computedState, TestResultState.Running);
 			assert.deepStrictEqual(getChangeSummary(), [
 				{ label: 'a', reason: TestResultItemChangeReason.ComputedStateChange },
 				{ label: 'aa', reason: TestResultItemChangeReason.OwnStateChange },
@@ -166,30 +167,30 @@ suite('Workbench - Test Results Service', () => {
 
 		test('ignores outside run', () => {
 			changed.clear();
-			r.updateState('id-b', 't', TestRunState.Running);
+			r.updateState('id-b', 't', TestResultState.Running);
 			assert.deepStrictEqual(r.counts, {
 				...makeEmptyCounts(),
-				[TestRunState.Queued]: 2,
-				[TestRunState.Unset]: 2,
+				[TestResultState.Queued]: 2,
+				[TestResultState.Unset]: 2,
 			});
 			assert.deepStrictEqual(r.getStateById('id-b'), undefined);
 		});
 
 		test('markComplete', () => {
-			r.setAllToState(TestRunState.Queued, 't', () => true);
-			r.updateState('id-aa', 't', TestRunState.Passed);
+			r.setAllToState(TestResultState.Queued, 't', () => true);
+			r.updateState('id-aa', 't', TestResultState.Passed);
 			changed.clear();
 
 			r.markComplete();
 
 			assert.deepStrictEqual(r.counts, {
 				...makeEmptyCounts(),
-				[TestRunState.Passed]: 1,
-				[TestRunState.Unset]: 3,
+				[TestResultState.Passed]: 1,
+				[TestResultState.Unset]: 3,
 			});
 
-			assert.deepStrictEqual(r.getStateById(tests.root.id)?.ownComputedState, TestRunState.Unset);
-			assert.deepStrictEqual(r.getStateById('id-aa')?.ownComputedState, TestRunState.Passed);
+			assert.deepStrictEqual(r.getStateById(tests.root.id)?.ownComputedState, TestResultState.Unset);
+			assert.deepStrictEqual(r.getStateById('id-aa')?.ownComputedState, TestResultState.Passed);
 		});
 	});
 
@@ -213,7 +214,7 @@ suite('Workbench - Test Results Service', () => {
 
 		test('serializes and re-hydrates', async () => {
 			results.push(r);
-			r.updateState('id-aa', 't', TestRunState.Passed);
+			r.updateState('id-aa', 't', TestResultState.Passed);
 			r.markComplete();
 			await timeout(10); // allow persistImmediately async to happen
 
@@ -270,7 +271,7 @@ suite('Workbench - Test Results Service', () => {
 			assert.deepStrictEqual(results.results, [r, r2]);
 		});
 
-		const makeHydrated = async (completedAt = 42, state = TestRunState.Passed) => new HydratedTestResult({
+		const makeHydrated = async (completedAt = 42, state = TestResultState.Passed) => new HydratedTestResult({
 			completedAt,
 			id: 'some-id',
 			tasks: [{ id: 't', running: false, name: undefined }],

src/vs/workbench/test/browser/api/extHostTesting.test.ts

@@ -11,9 +11,9 @@ import { mockObject, MockObject } from 'vs/base/test/common/mock';
 import { MainThreadTestingShape } from 'vs/workbench/api/common/extHost.protocol';
 import { TestRunConfigurationImpl, TestRunCoordinator, TestRunDto } from 'vs/workbench/api/common/extHostTesting';
 import * as convert from 'vs/workbench/api/common/extHostTypeConverters';
-import { TestMessage, TestRunConfigurationGroup } from 'vs/workbench/api/common/extHostTypes';
+import { TestMessage, TestResultState, TestRunConfigurationGroup } from 'vs/workbench/api/common/extHostTypes';
 import { TestDiffOpType, TestItemExpandState } from 'vs/workbench/contrib/testing/common/testCollection';
-import { TestItemImpl, TestResultState, testStubs } from 'vs/workbench/contrib/testing/common/testStubs';
+import { TestItemImpl, testStubs } from 'vs/workbench/contrib/testing/common/testStubs';
 import { TestSingleUseCollection } from 'vs/workbench/contrib/testing/test/common/ownedTestCollection';
 import type { TestItem, TestRunRequest } from 'vscode';
 
@@ -35,8 +35,8 @@ const assertTreesEqual = (a: TestItem | undefined, b: TestItem | undefined) => {
 
 	assert.deepStrictEqual(simplify(a), simplify(b));
 
-	const aChildren = [...a.children.keys()].slice().sort();
-	const bChildren = [...b.children.keys()].slice().sort();
+	const aChildren = a.children.all.map(c => c.id).sort();
+	const bChildren = b.children.all.map(c => c.id).sort();
 	assert.strictEqual(aChildren.length, bChildren.length, `expected ${a.label}.children.length == ${b.label}.children.length`);
 	aChildren.forEach(key => assertTreesEqual(a.children.get(key), b.children.get(key)));
 };
@@ -109,6 +109,16 @@ suite('ExtHost Testing', () => {
 			]);
 		});
 
+		test('parents are set correctly', () => {
+			single.expand(single.root.id, Infinity);
+			single.collectDiff();
+
+			const a = single.root.children.get('id-a')!;
+			const ab = a.children.get('id-ab')!;
+			assert.strictEqual(a.parent, undefined);
+			assert.strictEqual(ab.parent, a);
+		});
+
 		test('no-ops if items not changed', () => {
 			single.collectDiff();
 			assert.deepStrictEqual(single.collectDiff(), []);
@@ -129,19 +139,20 @@ suite('ExtHost Testing', () => {
 		test('removes children', () => {
 			single.expand(single.root.id, Infinity);
 			single.collectDiff();
-			single.root.children.get('id-a')!.dispose();
+			single.root.children.remove('id-a');
 
 			assert.deepStrictEqual(single.collectDiff(), [
 				[TestDiffOpType.Remove, 'id-a'],
 			]);
-			assert.deepStrictEqual([...single.tree].map(n => n.item.extId).sort(), [single.root.id, 'id-b']);
-			assert.strictEqual(single.itemToInternal.size, 2);
+			assert.deepStrictEqual([...single.tree].map(n => n.actual.id).sort(), [single.root.id, 'id-b']);
+			assert.strictEqual(single.tree.size, 2);
 		});
 
 		test('adds new children', () => {
 			single.expand(single.root.id, Infinity);
 			single.collectDiff();
-			const child = new TestItemImpl('id-ac', 'c', undefined, undefined, single.root.children.get('id-a'));
+			const child = new TestItemImpl('id-ac', 'c', undefined);
+			single.root.children.get('id-a')!.children.add(child);
 
 			assert.deepStrictEqual(single.collectDiff(), [
 				[TestDiffOpType.Add, {
@@ -152,10 +163,111 @@ suite('ExtHost Testing', () => {
 				}],
 			]);
 			assert.deepStrictEqual(
-				[...single.tree].map(n => n.item.extId).sort(),
+				[...single.tree].map(n => n.actual.id).sort(),
 				[single.root.id, 'id-a', 'id-aa', 'id-ab', 'id-ac', 'id-b'],
 			);
-			assert.strictEqual(single.itemToInternal.size, 6);
+			assert.strictEqual(single.tree.size, 6);
+		});
+
+		test('treats in-place replacement as mutation', () => {
+			single.expand(single.root.id, Infinity);
+			single.collectDiff();
+
+			const oldA = single.root.children.get('id-a')!;
+			const newA = new TestItemImpl('id-a', 'Hello world', undefined);
+			newA.children.all = oldA.children.all;
+			single.root.children.all = [
+				newA,
+				new TestItemImpl('id-b', single.root.children.get('id-b')!.label, undefined),
+			];
+
+			assert.deepStrictEqual(single.collectDiff(), [
+				[
+					TestDiffOpType.Update,
+					{ extId: 'id-a', expand: TestItemExpandState.Expanded, item: { label: 'Hello world' } },
+				],
+			]);
+
+			newA.label = 'still connected';
+			assert.deepStrictEqual(single.collectDiff(), [
+				[
+					TestDiffOpType.Update,
+					{ extId: 'id-a', item: { label: 'still connected' } }
+				],
+			]);
+
+			oldA.label = 'no longer connected';
+			assert.deepStrictEqual(single.collectDiff(), []);
+		});
+
+		test('treats in-place replacement as mutation deeply', () => {
+			single.expand(single.root.id, Infinity);
+			single.collectDiff();
+
+			const oldA = single.root.children.get('id-a')!;
+			const newA = new TestItemImpl('id-a', single.root.children.get('id-a')!.label, undefined);
+			const oldAA = oldA.children.get('id-aa')!;
+			const oldAB = oldA.children.get('id-ab')!;
+			const newAB = new TestItemImpl('id-ab', 'Hello world', undefined);
+			newA.children.all = [oldAA, newAB];
+			single.root.children.all = [newA, single.root.children.get('id-b')!];
+
+			assert.deepStrictEqual(single.collectDiff(), [
+				[
+					TestDiffOpType.Update,
+					{ extId: 'id-a', expand: TestItemExpandState.Expanded },
+				],
+				[
+					TestDiffOpType.Update,
+					{ extId: 'id-ab', item: { label: 'Hello world' } },
+				],
+			]);
+
+			oldAA.label = 'still connected1';
+			newAB.label = 'still connected2';
+			oldAB.label = 'not connected3';
+			assert.deepStrictEqual(single.collectDiff(), [
+				[
+					TestDiffOpType.Update,
+					{ extId: 'id-aa', item: { label: 'still connected1' } }
+				],
+				[
+					TestDiffOpType.Update,
+					{ extId: 'id-ab', item: { label: 'still connected2' } }
+				],
+			]);
+
+			assert.strictEqual(newAB.parent, newA);
+			assert.strictEqual(oldAA.parent, newA);
+			assert.deepStrictEqual(newA.parent, undefined);
+		});
+
+		test('moves an item to be a new child', () => {
+			single.collectDiff();
+			const b = single.root.children.get('id-b')!;
+			const a = single.root.children.get('id-a')!;
+			a.children.add(b);
+			assert.deepStrictEqual(single.collectDiff(), [
+				[
+					TestDiffOpType.Remove,
+					'id-b',
+				],
+				[
+					TestDiffOpType.Add,
+					{ controllerId: 'ctrlId', parent: 'id-a', expand: TestItemExpandState.NotExpandable, item: convert.TestItem.from(single.tree.get('id-b')!.actual) }
+				],
+			]);
+
+			b.label = 'still connected';
+			assert.deepStrictEqual(single.collectDiff(), [
+				[
+					TestDiffOpType.Update,
+					{ extId: 'id-b', item: { label: 'still connected' } }
+				],
+			]);
+
+			assert.deepStrictEqual(single.root.children.all, [single.root.children.get('id-a')]);
+			assert.deepStrictEqual(b.parent, a);
 		});
 	});
 
@@ -314,7 +426,7 @@ suite('ExtHost Testing', () => {
 			configuration = new TestRunConfigurationImpl(mockObject<MainThreadTestingShape, {}>(), 'ctrlId', 42, 'Do Run', TestRunConfigurationGroup.Run, () => { }, false);
 
 			req = {
-				tests: [single.root],
+				include: undefined,
 				exclude: [single.root.children.get('id-b')!],
 				configuration,
 			};
@@ -325,15 +437,15 @@ suite('ExtHost Testing', () => {
 				excludeExtIds: ['id-b'],
 				runId: 'run-id',
 				testIds: [single.root.id],
-			});
+			}, single);
 		});
 
 		test('tracks a run started from a main thread request', () => {
 			const tracker = c.prepareForMainThreadTestRun(req, dto, cts.token);
 			assert.strictEqual(tracker.isRunning, false);
 
-			const task1 = c.createTestRun('ctrl', req, 'run1', true);
-			const task2 = c.createTestRun('ctrl', req, 'run2', true);
+			const task1 = c.createTestRun('ctrl', single, req, 'run1', true);
+			const task2 = c.createTestRun('ctrl', single, req, 'run2', true);
 			assert.strictEqual(proxy.$startedExtensionTestRun.called, false);
 			assert.strictEqual(tracker.isRunning, true);
 
@@ -351,7 +463,7 @@ suite('ExtHost Testing', () => {
 		});
 
 		test('tracks a run started from an extension request', () => {
-			const task1 = c.createTestRun('ctrl', req, 'hello world', false);
+			const task1 = c.createTestRun('ctrl', single, req, 'hello world', false);
 
 			const tracker = Iterable.first(c.trackers)!;
 			assert.strictEqual(tracker.isRunning, true);
@@ -360,14 +472,14 @@ suite('ExtHost Testing', () => {
 					config: { group: 2, id: 42 },
 					controllerId: 'ctrl',
 					id: tracker.id,
-					tests: [single.root.id],
+					include: [single.root.id],
 					exclude: ['id-b'],
 					persist: false,
 				}]
 			]);
 
-			const task2 = c.createTestRun('ctrl', req, 'run2', true);
-			const task3Detached = c.createTestRun('ctrl', { ...req }, 'task3Detached', true);
+			const task2 = c.createTestRun('ctrl', single, req, 'run2', true);
+			const task3Detached = c.createTestRun('ctrl', single, { ...req }, 'task3Detached', true);
 
 			task1.end();
 			assert.strictEqual(proxy.$finishedExtensionTestRun.called, false);
@@ -381,7 +493,7 @@ suite('ExtHost Testing', () => {
 		});
 
 		test('adds tests to run smartly', () => {
-			const task1 = c.createTestRun('ctrl', req, 'hello world', false);
+			const task1 = c.createTestRun('ctrl', single, req, 'hello world', false);
 			const tracker = Iterable.first(c.trackers)!;
 			const expectedArgs: unknown[][] = [];
 			assert.deepStrictEqual(proxy.$addTestsToRun.args, expectedArgs);
@@ -416,7 +528,7 @@ suite('ExtHost Testing', () => {
 		});
 
 		test('guards calls after runs are ended', () => {
-			const task = c.createTestRun('ctrl', req, 'hello world', false);
+			const task = c.createTestRun('ctrl', single, req, 'hello world', false);
 			task.end();
 
 			task.setState(single.root, TestResultState.Passed);
@@ -431,9 +543,9 @@ suite('ExtHost Testing', () => {
 		test('excludes tests outside tree or explicitly excluded', () => {
 			single.expand(single.root.id, Infinity);
 
-			const task = c.createTestRun('ctrl', {
+			const task = c.createTestRun('ctrl', single, {
 				configuration,
-				tests: [single.root.children.get('id-a')!],
+				include: [single.root.children.get('id-a')!],
 				exclude: [single.root.children.get('id-a')!.children.get('id-aa')!],
 			}, 'hello world', false);