fix: copilot feedback

Author: tsck

tests/unit/toolBase.test.ts

@@ -15,11 +15,7 @@ import type { Server } from "../../src/server.js";
 import type { TelemetryToolMetadata, ToolEvent } from "../../src/telemetry/types.js";
 import type { PreviewFeature } from "../../src/common/schemas.js";
 import { UIRegistry } from "../../src/ui/registry/index.js";
-
-function expectDefined<T>(arg: T): asserts arg is Exclude<T, undefined | null> {
-    expect(arg).toBeDefined();
-    expect(arg).not.toBeNull();
-}
+import { expectDefined } from "../integration/helpers.js";
 
 describe("ToolBase", () => {
     let mockSession: Session;