Tests: silence expected console.warn in require-test output

Summary:
Metro's `require` polyfill is expected to print require cycle warnings, and when testing cycle scenarios this spams the Jest output (except in the one case where we explicitly mock `console.warn` to check the warning).

This diff lifts the `console.warn` spy up so as to silence it.

Changelog: Internal

Reviewed By: jacdebug

Differential Revision: D44505719

fbshipit-source-id: 9ca845aa218d49896dcc2ec4723b403513302d80

packages/metro-runtime/src/polyfills/__tests__/require-test.js

@@ -29,6 +29,8 @@ function createModule(
   );
 }
 
+const consoleWarnSpy = jest.spyOn(console, 'warn').mockImplementation(() => {});
+
 describe('require', () => {
   const moduleSystemCode = (() => {
     const rawCode = fs.readFileSync(require.resolve('../require'), 'utf8');
@@ -85,6 +87,7 @@ describe('require', () => {
 
   beforeEach(() => {
     moduleSystem = {};
+    consoleWarnSpy.mockClear();
   });
 
   it('does not need any babel helper logic', () => {
@@ -567,15 +570,10 @@ describe('require', () => {
         },
       );
 
-      const warn = console.warn;
-      console.warn = jest.fn();
-
       expect(moduleSystem.__r('foo.js')).toEqual('Hi!');
-      expect(console.warn).toHaveBeenCalledWith(
+      expect(consoleWarnSpy).toHaveBeenCalledWith(
         'Requiring module "foo.js" by name is only supported for debugging purposes and will BREAK IN PRODUCTION!',
       );
-
-      console.warn = warn;
     });
 
     it('throws an error when requiring an incorrect verboseNames in dev mode', () => {