fix(signature-v4): mock Date in SigV4 tests

packages/signature-v4/package.json

@@ -11,7 +11,6 @@
     "build:es": "tsc -p tsconfig.es.json",
     "build:types": "tsc -p tsconfig.types.json",
     "downlevel-dts": "downlevel-dts dist-types dist-types/ts3.4",
-    "pretest": "yarn build",
     "test": "jest --coverage"
   },
   "author": {

packages/signature-v4/src/SignatureV4.spec.ts

@@ -709,21 +709,26 @@ describe("SignatureV4", () => {
   });
 
   describe("ambient Date usage", () => {
-    const knownDate = new Date("1999-12-31T23:59:59.999Z");
+    let dateSpy;
+    const mockDate = new Date();
 
     beforeEach(() => {
-      Date.now = jest.fn().mockReturnValue(knownDate) as any;
+      dateSpy = jest.spyOn(global, "Date").mockImplementation(() => mockDate as unknown as string);
+    });
+
+    afterEach(() => {
+      expect(dateSpy).toHaveBeenCalledTimes(1);
+      jest.clearAllMocks();
     });
 
     it("should use the current date for presigning if no signing date was supplied", async () => {
-      const date = new Date();
       const { query } = await signer.presign(minimalRequest);
-      expect((query as any)[AMZ_DATE_QUERY_PARAM]).toBe(iso8601(date).replace(/[\-:]/g, ""));
+      expect((query as any)[AMZ_DATE_QUERY_PARAM]).toBe(iso8601(mockDate).replace(/[\-:]/g, ""));
     });
 
     it("should use the current date for signing if no signing date supplied", async () => {
       const { headers } = await signer.sign(minimalRequest);
-      expect(headers[AMZ_DATE_HEADER]).toBe(iso8601(new Date()).replace(/[\-:]/g, ""));
+      expect(headers[AMZ_DATE_HEADER]).toBe(iso8601(mockDate).replace(/[\-:]/g, ""));
     });
   });
 });