diff --git a/extensions/markdown/src/test/tableOfContentsProvider.test.ts b/extensions/markdown/src/test/tableOfContentsProvider.test.ts
index f59a5c29697d2ce520e10fabd42f24ddc81d356d..3c200483ae26edc38e7129c73dbe1e073700a580 100644
--- a/extensions/markdown/src/test/tableOfContentsProvider.test.ts
+++ b/extensions/markdown/src/test/tableOfContentsProvider.test.ts
@@ -9,14 +9,69 @@ import * as vscode from 'vscode';
 import { TableOfContentsProvider } from '../tableOfContentsProvider';
 import { MarkdownEngine } from '../markdownEngine';
 
+const testFileName = vscode.Uri.parse('test.md');
+
 suite('markdown.TableOfContentsProvider', () => {
-	test('Should not return anything for empty document', async () => {
-		const doc = new InMemoryDocument(vscode.Uri.parse('test.md'), '');
+	test('Lookup should not return anything for empty document', async () => {
+		const doc = new InMemoryDocument(testFileName, '');
 		const provider = new TableOfContentsProvider(new MarkdownEngine(), doc);
 
 		assert.strictEqual(await provider.lookup(''), undefined);
 		assert.strictEqual(await provider.lookup('foo'), undefined);
 	});
+
+	test('Lookup should not return anything for document with no headers', async () => {
+		const doc = new InMemoryDocument(testFileName, 'a *b*\nc');
+		const provider = new TableOfContentsProvider(new MarkdownEngine(), doc);
+
+		assert.strictEqual(await provider.lookup(''), undefined);
+		assert.strictEqual(await provider.lookup('foo'), undefined);
+		assert.strictEqual(await provider.lookup('a'), undefined);
+		assert.strictEqual(await provider.lookup('b'), undefined);
+	});
+
+	test('Lookup should return basic #header', async () => {
+		const doc = new InMemoryDocument(testFileName, `# a\nx\n# c`);
+		const provider = new TableOfContentsProvider(new MarkdownEngine(), doc);
+
+		{
+			const entry = await provider.lookup('a');
+			assert.ok(entry);
+			assert.strictEqual(entry!.line, 0);
+		}
+		{
+			assert.strictEqual(await provider.lookup('x'), undefined);
+		}
+		{
+			const entry = await provider.lookup('c');
+			assert.ok(entry);
+			assert.strictEqual(entry!.line, 2);
+		}
+	});
+
+	test('Lookups should be case in-sensitive', async () => {
+		const doc = new InMemoryDocument(testFileName, `# fOo\n`);
+		const provider = new TableOfContentsProvider(new MarkdownEngine(), doc);
+
+		assert.strictEqual((await provider.lookup('fOo'))!.line, 0);
+		assert.strictEqual((await provider.lookup('foo'))!.line, 0);
+		assert.strictEqual((await provider.lookup('FOO'))!.line, 0);
+	});
+
+	test('Lookups should ignore leading and trailing white-space, and collapse internal whitespace', async () => {
+		const doc = new InMemoryDocument(testFileName, `#      f o  o    \n`);
+		const provider = new TableOfContentsProvider(new MarkdownEngine(), doc);
+
+		assert.strictEqual((await provider.lookup('f o  o'))!.line, 0);
+		assert.strictEqual((await provider.lookup('  f o  o'))!.line, 0);
+		assert.strictEqual((await provider.lookup('  f o  o  '))!.line, 0);
+		assert.strictEqual((await provider.lookup('f o o'))!.line, 0);
+		assert.strictEqual((await provider.lookup('f o       o'))!.line, 0);
+
+		assert.strictEqual(await provider.lookup('f'), undefined);
+		assert.strictEqual(await provider.lookup('foo'), undefined);
+		assert.strictEqual(await provider.lookup('fo o'), undefined);
+	});
 });
 
 class InMemoryDocument implements vscode.TextDocument {
@@ -24,9 +79,9 @@ class InMemoryDocument implements vscode.TextDocument {
 
 	constructor(
 		public readonly uri: vscode.Uri,
-		contents: string
+		private readonly _contents: string
 	) {
-		this._lines = contents.split(/\n/g);
+		this._lines = this._contents.split(/\n/g);
 	}
 
 	fileName: string = '';
@@ -54,11 +109,11 @@ class InMemoryDocument implements vscode.TextDocument {
 	offsetAt(_position: vscode.Position): never {
 		throw new Error('Method not implemented.');
 	}
-	positionAt(_offset: number): never{
+	positionAt(_offset: number): never {
 		throw new Error('Method not implemented.');
 	}
-	getText(_range?: vscode.Range | undefined): never {
-		throw new Error('Method not implemented.');
+	getText(_range?: vscode.Range | undefined): string {
+		return this._contents;
 	}
 	getWordRangeAtPosition(_position: vscode.Position, _regex?: RegExp | undefined): never {
 		throw new Error('Method not implemented.');