chore(integ-runner): fix a race in the unit tests (#22960)

We weren't actually mocking the `writeFileSync` call we thought we were, as the internal libraries call `fs.writeFileSync`, but we were mocking `fs-extra.writeFileSync`.


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*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: rix0rrr

packages/@aws-cdk/integ-runner/test/runner/integ-test-runner.test.ts

@@ -1,4 +1,5 @@
 import * as child_process from 'child_process';
+import * as builtinFs from 'fs';
 import { Manifest } from '@aws-cdk/cloud-assembly-schema';
 import { AVAILABILITY_ZONE_FALLBACK_CONTEXT_KEY } from '@aws-cdk/cx-api';
 import * as fs from 'fs-extra';
@@ -24,7 +25,9 @@ beforeEach(() => {
   });
   jest.spyOn(fs, 'moveSync').mockImplementation(() => { return true; });
   removeSyncMock = jest.spyOn(fs, 'removeSync').mockImplementation(() => { return true; });
-  jest.spyOn(fs, 'writeFileSync').mockImplementation(() => { return true; });
+
+  // fs-extra delegates to the built-in one, this also catches calls done directly
+  jest.spyOn(builtinFs, 'writeFileSync').mockImplementation(() => { return true; });
 });
 
 afterEach(() => {

packages/@aws-cdk/integ-runner/test/runner/snapshot-test-runner.test.ts

@@ -1,4 +1,5 @@
 import * as child_process from 'child_process';
+import * as builtinFs from 'fs';
 import * as path from 'path';
 import * as fs from 'fs-extra';
 import { IntegSnapshotRunner, IntegTest } from '../../lib/runner';
@@ -24,8 +25,10 @@ beforeEach(() => {
   jest.spyOn(process.stdout, 'write').mockImplementation(() => { return true; });
   jest.spyOn(fs, 'moveSync').mockImplementation(() => { return true; });
   jest.spyOn(fs, 'removeSync').mockImplementation(() => { return true; });
-  jest.spyOn(fs, 'writeFileSync').mockImplementation(() => { return true; });
-  jest.spyOn(fs, 'rmdirSync').mockImplementation(() => { return true; });
+
+  // fs-extra delegates to the built-in one, this also catches calls done directly
+  jest.spyOn(builtinFs, 'writeFileSync').mockImplementation(() => { return true; });
+  jest.spyOn(builtinFs, 'rmdirSync').mockImplementation(() => { return true; });
 });
 
 afterEach(() => {

packages/@aws-cdk/integ-runner/test/workers/integ-worker.test.ts

@@ -1,4 +1,5 @@
 import * as child_process from 'child_process';
+import * as builtinFs from 'fs';
 import * as path from 'path';
 import * as fs from 'fs-extra';
 import * as workerpool from 'workerpool';
@@ -13,10 +14,13 @@ beforeAll(() => {
 beforeEach(() => {
   jest.spyOn(fs, 'moveSync').mockImplementation(() => { return true; });
   jest.spyOn(fs, 'emptyDirSync').mockImplementation(() => { return true; });
-  jest.spyOn(fs, 'unlinkSync').mockImplementation(() => { return true; });
   jest.spyOn(fs, 'removeSync').mockImplementation(() => { return true; });
-  jest.spyOn(fs, 'rmdirSync').mockImplementation(() => { return true; });
-  jest.spyOn(fs, 'writeFileSync').mockImplementation(() => { return true; });
+
+  // fs-extra delegates to the built-in one, this also catches calls done directly
+  jest.spyOn(builtinFs, 'rmdirSync').mockImplementation(() => { return true; });
+  jest.spyOn(builtinFs, 'writeFileSync').mockImplementation(() => { return true; });
+  jest.spyOn(builtinFs, 'unlinkSync').mockImplementation(() => { return true; });
+
   spawnSyncMock = jest.spyOn(child_process, 'spawnSync')
     .mockReturnValueOnce({
       status: 0,