diff --git a/packages/cursorless-vscode/src/constructTestHelpers.ts b/packages/cursorless-vscode/src/constructTestHelpers.ts
index 3d2941dd2a..a68539edb0 100644
--- a/packages/cursorless-vscode/src/constructTestHelpers.ts
+++ b/packages/cursorless-vscode/src/constructTestHelpers.ts
@@ -20,6 +20,7 @@ import { TestHelpers } from "@cursorless/vscode-common";
 import * as vscode from "vscode";
 import { VscodeIDE } from "./ide/vscode/VscodeIDE";
 import { toVscodeEditor } from "./ide/vscode/toVscodeEditor";
+import { vscodeApi } from "./vscodeApi";
 
 export function constructTestHelpers(
   commandServerApi: CommandServerApi | null,
@@ -74,5 +75,6 @@ export function constructTestHelpers(
     },
     hatTokenMap,
     runIntegrationTests,
+    vscodeApi,
   };
 }
diff --git a/packages/cursorless-vscode/src/vscodeApi.ts b/packages/cursorless-vscode/src/vscodeApi.ts
new file mode 100644
index 0000000000..8275a485c3
--- /dev/null
+++ b/packages/cursorless-vscode/src/vscodeApi.ts
@@ -0,0 +1,19 @@
+import { workspace, window } from "vscode";
+import { VscodeApi } from "@cursorless/vscode-common";
+
+/**
+ * A very thin wrapper around the VSCode API that allows us to mock it for
+ * testing. This is necessary because the test harness gets bundled separately
+ * from the extension code, so if we just import the VSCode API directly from
+ * the extension code, and from the test harness, we'll end up with two copies
+ * of the VSCode API, so the mocks won't work.
+ */
+export const vscodeApi: VscodeApi = {
+  workspace,
+  window,
+  editor: {
+    setDecorations(editor, ...args) {
+      return editor.setDecorations(...args);
+    },
+  },
+};
diff --git a/packages/vscode-common/src/VscodeApi.ts b/packages/vscode-common/src/VscodeApi.ts
new file mode 100644
index 0000000000..34048bb2b0
--- /dev/null
+++ b/packages/vscode-common/src/VscodeApi.ts
@@ -0,0 +1,21 @@
+import { workspace, window, TextEditor } from "vscode";
+
+/**
+ * Subset of VSCode api that we need to be able to mock for testing
+ */
+export interface VscodeApi {
+  workspace: typeof workspace;
+  window: typeof window;
+
+  /**
+   * Wrapper around editor api for easy mocking.  Provides various
+   * {@link TextEditor} methods as static functions which take a text editor as
+   * their first argument.
+   */
+  editor: {
+    setDecorations(
+      editor: TextEditor,
+      ...args: Parameters<TextEditor["setDecorations"]>
+    ): ReturnType<TextEditor["setDecorations"]>;
+  };
+}
diff --git a/packages/vscode-common/src/getExtensionApi.ts b/packages/vscode-common/src/getExtensionApi.ts
index 6c083ed85b..079f85b704 100644
--- a/packages/vscode-common/src/getExtensionApi.ts
+++ b/packages/vscode-common/src/getExtensionApi.ts
@@ -13,6 +13,7 @@ import type {
 } from "@cursorless/common";
 import * as vscode from "vscode";
 import type { Language, SyntaxNode, Tree } from "web-tree-sitter";
+import { VscodeApi } from "./VscodeApi";
 
 export interface TestHelpers {
   ide: NormalizedIDE;
@@ -42,6 +43,11 @@ export interface TestHelpers {
   ): Promise<TestCaseSnapshot>;
 
   runIntegrationTests(): Promise<void>;
+
+  /**
+   * A thin wrapper around the VSCode API that allows us to mock it for testing.
+   */
+  vscodeApi: VscodeApi;
 }
 
 export interface CursorlessApi {
diff --git a/packages/vscode-common/src/index.ts b/packages/vscode-common/src/index.ts
index 15435d5cc6..de3a299986 100644
--- a/packages/vscode-common/src/index.ts
+++ b/packages/vscode-common/src/index.ts
@@ -3,3 +3,4 @@ export * from "./notebook";
 export * from "./testUtil/openNewEditor";
 export * from "./vscodeUtil";
 export * from "./runCommand";
+export * from "./VscodeApi";