diff --git a/src/vs/workbench/test/node/api/extHostDiagnostics.test.ts b/src/vs/workbench/test/node/api/extHostDiagnostics.test.ts
index 9f7725fe1f1fb8c13cbfa0a3a313ceab6082d69e..ab1dd37b04133ca18512e3786e2f799169febc95 100644
--- a/src/vs/workbench/test/node/api/extHostDiagnostics.test.ts
+++ b/src/vs/workbench/test/node/api/extHostDiagnostics.test.ts
@@ -8,7 +8,7 @@
 import * as assert from 'assert';
 import URI from 'vs/base/common/uri';
 import {DiagnosticCollection} from 'vs/workbench/api/node/extHostDiagnostics';
-import {Diagnostic, Range, DiagnosticSeverity} from 'vs/workbench/api/node/extHostTypes';
+import {Diagnostic, Range} from 'vs/workbench/api/node/extHostTypes';
 import {MainThreadDiagnosticsShape} from 'vs/workbench/api/node/extHost.protocol';
 import {TPromise} from 'vs/base/common/winjs.base';
 import {IMarkerData} from 'vs/platform/markers/common/markers';
@@ -159,4 +159,20 @@ suite('ExtHostDiagnostics', () => {
 	});
 
 
+	test('diagnostic capping', function () {
+
+		let lastEntries: [URI, IMarkerData[]][];
+		let collection = new DiagnosticCollection('test', new class extends DiagnosticsShape {
+			$changeMany(owner: string, entries: [URI, IMarkerData[]][]): TPromise<any> {
+				lastEntries = entries;
+				return super.$changeMany(owner, entries);
+			}
+		});
+		let uri = URI.parse('aa:bb');
+
+		collection.set(uri, new Array(500).map((value, i) => new Diagnostic(new Range(i, 0, i + 1, 0), `error#${i}`)));
+		assert.equal(collection.get(uri).length, 500);
+		assert.equal(lastEntries.length, 1);
+		assert.equal(lastEntries[0][1].length, 250);
+	});
 });
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