diff --git a/src/vs/workbench/api/common/extHostTypeConverters.ts b/src/vs/workbench/api/common/extHostTypeConverters.ts
index e47c784fa9f06f..cc43c4ad3e8e75 100644
--- a/src/vs/workbench/api/common/extHostTypeConverters.ts
+++ b/src/vs/workbench/api/common/extHostTypeConverters.ts
@@ -33,7 +33,7 @@ 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';
 import * as search from 'vs/workbench/contrib/search/common/search';
-import { CoverageDetails, DetailType, ICoveredCount, IFileCoverage, ISerializedTestResults, ITestErrorMessage, ITestItem, ITestItemContext, ITestTag, SerializedTestErrorMessage, SerializedTestResultItem, TestMessageType } from 'vs/workbench/contrib/testing/common/testCollection';
+import { CoverageDetails, denamespaceTestTag, DetailType, ICoveredCount, IFileCoverage, ISerializedTestResults, ITestErrorMessage, ITestItem, ITestItemContext, ITestTag, namespaceTestTag, SerializedTestErrorMessage, SerializedTestResultItem, TestMessageType } from 'vs/workbench/contrib/testing/common/testCollection';
 import { TestId } from 'vs/workbench/contrib/testing/common/testId';
 import { EditorGroupColumn } from 'vs/workbench/services/editor/common/editorGroupColumn';
 import { ACTIVE_GROUP, SIDE_GROUP } from 'vs/workbench/services/editor/common/editorService';
@@ -1700,17 +1700,9 @@ export namespace TestMessage {
 }
 
 export namespace TestTag {
-	const enum Constants {
-		Delimiter = '\0',
-	}
-
-	export const namespace = (ctrlId: string, tagId: string) =>
-		ctrlId + Constants.Delimiter + tagId;
+	export const namespace = namespaceTestTag;
 
-	export const denamespace = (namespaced: string) => {
-		const index = namespaced.indexOf(Constants.Delimiter);
-		return { ctrlId: namespaced.slice(0, index), tagId: namespaced.slice(index + 1) };
-	};
+	export const denamespace = denamespaceTestTag;
 }
 
 export namespace TestItem {
diff --git a/src/vs/workbench/contrib/testing/browser/testingExplorerFilter.ts b/src/vs/workbench/contrib/testing/browser/testingExplorerFilter.ts
index d2afbf5bd3fb67..23832ee3205393 100644
--- a/src/vs/workbench/contrib/testing/browser/testingExplorerFilter.ts
+++ b/src/vs/workbench/contrib/testing/browser/testingExplorerFilter.ts
@@ -17,11 +17,11 @@ import { IContextMenuService } from 'vs/platform/contextview/browser/contextView
 import { IInstantiationService } from 'vs/platform/instantiation/common/instantiation';
 import { StorageScope, StorageTarget } from 'vs/platform/storage/common/storage';
 import { IThemeService, ThemeIcon } from 'vs/platform/theme/common/themeService';
-import { TestTag } from 'vs/workbench/api/common/extHostTypeConverters';
 import { attachSuggestEnabledInputBoxStyler, ContextScopedSuggestEnabledInputWithHistory, SuggestEnabledInputWithHistory, SuggestResultsProvider } from 'vs/workbench/contrib/codeEditor/browser/suggestEnabledInput/suggestEnabledInput';
 import { testingFilterIcon } from 'vs/workbench/contrib/testing/browser/icons';
 import { Testing } from 'vs/workbench/contrib/testing/common/constants';
 import { StoredValue } from 'vs/workbench/contrib/testing/common/storedValue';
+import { denamespaceTestTag } from 'vs/workbench/contrib/testing/common/testCollection';
 import { ITestExplorerFilterState, TestFilterTerm } from 'vs/workbench/contrib/testing/common/testExplorerFilterState';
 import { ITestService } from 'vs/workbench/contrib/testing/common/testService';
 
@@ -74,7 +74,7 @@ export class TestingExplorerFilter extends BaseActionViewItem {
 				provideResults: () => [
 					...Object.entries(testFilterDescriptions).map(([label, detail]) => ({ label, detail })),
 					...Iterable.map(this.testService.collection.tags.values(), tag => {
-						const { ctrlId, tagId } = TestTag.denamespace(tag.id);
+						const { ctrlId, tagId } = denamespaceTestTag(tag.id);
 						const insertText = `@${ctrlId}:${tagId}`;
 						return ({
 							label: `@${ctrlId}:${tagId}`,
diff --git a/src/vs/workbench/contrib/testing/browser/testingProgressUiService.ts b/src/vs/workbench/contrib/testing/browser/testingProgressUiService.ts
index ddbbd0b9e6d394..77ac8c24841b04 100644
--- a/src/vs/workbench/contrib/testing/browser/testingProgressUiService.ts
+++ b/src/vs/workbench/contrib/testing/browser/testingProgressUiService.ts
@@ -10,10 +10,10 @@ import { localize } from 'vs/nls';
 import { IConfigurationService } from 'vs/platform/configuration/common/configuration';
 import { createDecorator, IInstantiationService } from 'vs/platform/instantiation/common/instantiation';
 import { ProgressLocation, UnmanagedProgress } from 'vs/platform/progress/common/progress';
-import { TestResultState } from 'vs/workbench/api/common/extHostTypes';
 import { ViewContainerLocation } from 'vs/workbench/common/views';
 import { AutoOpenTesting, getTestingConfiguration, TestingConfigKeys } from 'vs/workbench/contrib/testing/common/configuration';
 import { Testing } from 'vs/workbench/contrib/testing/common/constants';
+import { TestResultState } from 'vs/workbench/contrib/testing/common/testCollection';
 import { isFailedState } from 'vs/workbench/contrib/testing/common/testingStates';
 import { LiveTestResult, TestResultItemChangeReason, TestStateCount } from 'vs/workbench/contrib/testing/common/testResult';
 import { ITestResultService } from 'vs/workbench/contrib/testing/common/testResultService';
diff --git a/src/vs/workbench/contrib/testing/common/testCollection.ts b/src/vs/workbench/contrib/testing/common/testCollection.ts
index 31a63d028178b9..1bb6f1dcb88046 100644
--- a/src/vs/workbench/contrib/testing/common/testCollection.ts
+++ b/src/vs/workbench/contrib/testing/common/testCollection.ts
@@ -8,7 +8,7 @@ import { MarshalledId } from 'vs/base/common/marshalling';
 import { URI } from 'vs/base/common/uri';
 import { IPosition } from 'vs/editor/common/core/position';
 import { IRange, Range } from 'vs/editor/common/core/range';
-import { ILocationDto } from 'vs/workbench/api/common/extHost.protocol';
+import { Dto } from 'vs/workbench/services/extensions/common/proxyIdentifier';
 
 export const enum TestResultState {
 	Unset = 0,
@@ -112,7 +112,7 @@ export interface ITestErrorMessage {
 	location: IRichLocation | undefined;
 }
 
-export type SerializedTestErrorMessage = Omit<ITestErrorMessage, 'location'> & { location?: ILocationDto };
+export type SerializedTestErrorMessage = Omit<ITestErrorMessage, 'location'> & { location?: Dto<Location> };
 
 export interface ITestOutputMessage {
 	message: string;
@@ -121,7 +121,7 @@ export interface ITestOutputMessage {
 	location: IRichLocation | undefined;
 }
 
-export type SerializedTestOutputMessage = Omit<ITestOutputMessage, 'location'> & { location?: ILocationDto };
+export type SerializedTestOutputMessage = Omit<ITestOutputMessage, 'location'> & { location?: Dto<Location> };
 
 export type SerializedTestMessage = SerializedTestErrorMessage | SerializedTestOutputMessage;
 
@@ -143,6 +143,16 @@ export interface ITestTag {
 	id: string;
 }
 
+const testTagDelimiter = '\0';
+
+export const namespaceTestTag =
+	(ctrlId: string, tagId: string) => ctrlId + testTagDelimiter + tagId;
+
+export const denamespaceTestTag = (namespaced: string) => {
+	const index = namespaced.indexOf(testTagDelimiter);
+	return { ctrlId: namespaced.slice(0, index), tagId: namespaced.slice(index + 1) };
+};
+
 export interface ITestTagDisplayInfo {
 	id: string;
 	ctrlLabel: string;
diff --git a/src/vs/workbench/contrib/testing/common/testExplorerFilterState.ts b/src/vs/workbench/contrib/testing/common/testExplorerFilterState.ts
index bff4bd12c716f0..2f5f78039ca140 100644
--- a/src/vs/workbench/contrib/testing/common/testExplorerFilterState.ts
+++ b/src/vs/workbench/contrib/testing/common/testExplorerFilterState.ts
@@ -5,8 +5,8 @@
 import { Emitter, Event } from 'vs/base/common/event';
 import { splitGlobAware } from 'vs/base/common/glob';
 import { createDecorator } from 'vs/platform/instantiation/common/instantiation';
-import { TestTag } from 'vs/workbench/api/common/extHostTypeConverters';
 import { IObservableValue, MutableObservableValue } from 'vs/workbench/contrib/testing/common/observableValue';
+import { namespaceTestTag } from 'vs/workbench/contrib/testing/common/testCollection';
 
 export interface ITestExplorerFilterState {
 	_serviceBrand: undefined;
@@ -134,9 +134,9 @@ export class TestExplorerFilterState implements ITestExplorerFilterState {
 				}
 
 				if (match[0].startsWith('!')) {
-					this.excludeTags.add(TestTag.namespace(match[1], tagId));
+					this.excludeTags.add(namespaceTestTag(match[1], tagId));
 				} else {
-					this.includeTags.add(TestTag.namespace(match[1], tagId));
+					this.includeTags.add(namespaceTestTag(match[1], tagId));
 				}
 				nextIndex++;
 			}