diff --git a/extensions/diffs/src/tool-render-output.test.ts b/extensions/diffs/src/tool-render-output.test.ts
index 2849986a9d3..2dadb1a3048 100644
--- a/extensions/diffs/src/tool-render-output.test.ts
+++ b/extensions/diffs/src/tool-render-output.test.ts
@@ -68,7 +68,7 @@ describe("diffs tool rendered output guards", () => {
     });
 
     expect(screenshotter.screenshotHtml).toHaveBeenCalledTimes(1);
-    expect((result?.details as Record<string, unknown>).filePath).toEqual(expect.any(String));
+    expect((result?.details as Record<string, unknown>).filePath).toMatch(/preview\.png$/);
   });
 });
 
diff --git a/extensions/diffs/src/tool.test.ts b/extensions/diffs/src/tool.test.ts
index 1a5eab936e2..cefa9518278 100644
--- a/extensions/diffs/src/tool.test.ts
+++ b/extensions/diffs/src/tool.test.ts
@@ -190,8 +190,10 @@ describe("diffs tool", () => {
     });
 
     expectArtifactOnlyFileResult(screenshotter, result);
-    expect((result?.details as Record<string, unknown>).artifactId).toEqual(expect.any(String));
-    expect((result?.details as Record<string, unknown>).expiresAt).toEqual(expect.any(String));
+    expect(requireString(readDetails(result).artifactId, "artifactId")).toMatch(/^[a-f0-9]{20}$/u);
+    expect(requireString(readDetails(result).expiresAt, "expiresAt")).toMatch(
+      /^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}Z$/u,
+    );
   });
 
   it("honors ttlSeconds for artifact-only file output", async () => {