diff --git a/extensions/diffs/src/tool.test.ts b/extensions/diffs/src/tool.test.ts
index 416bdf8dc14..1e939c60390 100644
--- a/extensions/diffs/src/tool.test.ts
+++ b/extensions/diffs/src/tool.test.ts
@@ -135,9 +135,7 @@ describe("diffs tool", () => {
       mode: "file",
     });
 
-    expect(screenshotter.screenshotHtml).toHaveBeenCalledTimes(1);
-    expect((result?.details as Record<string, unknown>).mode).toBe("file");
-    expect((result?.details as Record<string, unknown>).viewerUrl).toBeUndefined();
+    expectArtifactOnlyFileResult(screenshotter, result);
   });
 
   it("honors ttlSeconds for artifact-only file output", async () => {
@@ -227,9 +225,7 @@ describe("diffs tool", () => {
       after: "two\n",
     });
 
-    expect(screenshotter.screenshotHtml).toHaveBeenCalledTimes(1);
-    expect((result?.details as Record<string, unknown>).mode).toBe("file");
-    expect((result?.details as Record<string, unknown>).viewerUrl).toBeUndefined();
+    expectArtifactOnlyFileResult(screenshotter, result);
   });
 
   it("falls back to view output when both mode cannot render an image", async () => {
@@ -434,6 +430,15 @@ function createToolWithScreenshotter(
   });
 }
 
+function expectArtifactOnlyFileResult(
+  screenshotter: DiffScreenshotter,
+  result: { details?: Record<string, unknown> } | null | undefined,
+) {
+  expect(screenshotter.screenshotHtml).toHaveBeenCalledTimes(1);
+  expect((result?.details as Record<string, unknown>).mode).toBe("file");
+  expect((result?.details as Record<string, unknown>).viewerUrl).toBeUndefined();
+}
+
 function createPngScreenshotter(
   params: {
     assertHtml?: (html: string) => void;