chore: use for..of instead of forEach (jestjs#14517)

.eslintrc.cjs

@@ -595,6 +595,7 @@ module.exports = {
     yoda: 'off',
 
     'unicorn/explicit-length-check': 'error',
+    'unicorn/no-array-for-each': 'error',
     'unicorn/no-negated-condition': 'error',
     'unicorn/prefer-default-parameters': 'error',
     'unicorn/prefer-includes': 'error',

e2e/MockStdinWatchPlugin.js

@@ -20,7 +20,7 @@ class MockStdinWatchPlugin {
   apply(jestHooks) {
     jestHooks.onTestRunComplete(() => {
       const {keys} = this._config.input.shift();
-      keys.forEach(key => this._stdin.emit('data', key));
+      for (const key of keys) this._stdin.emit('data', key);
     });
   }
 }

e2e/Utils.ts

@@ -128,7 +128,7 @@ export const writeFiles = (
   files: {[filename: string]: string},
 ) => {
   fs.mkdirSync(directory, {recursive: true});
-  Object.keys(files).forEach(fileOrPath => {
+  for (const fileOrPath of Object.keys(files)) {
     const dirname = path.dirname(fileOrPath);
 
     if (dirname !== '/') {
@@ -138,15 +138,15 @@ export const writeFiles = (
       path.resolve(directory, ...fileOrPath.split('/')),
       dedent(files[fileOrPath]),
     );
-  });
+  }
 };
 
 export const writeSymlinks = (
   directory: string,
   symlinks: {[existingFile: string]: string},
 ) => {
   fs.mkdirSync(directory, {recursive: true});
-  Object.keys(symlinks).forEach(fileOrPath => {
+  for (const fileOrPath of Object.keys(symlinks)) {
     const symLinkPath = symlinks[fileOrPath];
     const dirname = path.dirname(symLinkPath);
 
@@ -158,7 +158,7 @@ export const writeSymlinks = (
       path.resolve(directory, ...symLinkPath.split('/')),
       'junction',
     );
-  });
+  }
 };
 
 const NUMBER_OF_TESTS_TO_FORCE_USING_WORKERS = 25;

e2e/__tests__/coverageRemapping.test.ts

@@ -27,11 +27,11 @@ it('maps code coverage against original source', () => {
   const coverageMap = JSON.parse(readFileSync(coverageMapFile, 'utf-8'));
 
   // reduce absolute paths embedded in the coverage map to just filenames
-  Object.keys(coverageMap).forEach(filename => {
+  for (const filename of Object.keys(coverageMap)) {
     coverageMap[filename].path = path.basename(coverageMap[filename].path);
     delete coverageMap[filename].hash;
     coverageMap[path.basename(filename)] = coverageMap[filename];
     delete coverageMap[filename];
-  });
+  }
   expect(coverageMap).toMatchSnapshot();
 });

e2e/__tests__/coverageTransformInstrumented.test.ts

@@ -27,11 +27,11 @@ it('code coverage for transform instrumented code', () => {
   const coverageMap = JSON.parse(readFileSync(coverageMapFile, 'utf-8'));
 
   // reduce absolute paths embedded in the coverage map to just filenames
-  Object.keys(coverageMap).forEach(filename => {
+  for (const filename of Object.keys(coverageMap)) {
     coverageMap[filename].path = path.basename(coverageMap[filename].path);
     delete coverageMap[filename].hash;
     coverageMap[path.basename(filename)] = coverageMap[filename];
     delete coverageMap[filename];
-  });
+  }
   expect(coverageMap).toMatchSnapshot();
 });

e2e/__tests__/errorOnDeprecated.test.ts

@@ -31,7 +31,7 @@ const SHOULD_NOT_PASS_IN_JEST = new Set([
   'spyOnProperty.test.js',
 ]);
 
-testFiles.forEach(testFile => {
+for (const testFile of testFiles) {
   test(`${testFile} errors in errorOnDeprecated mode`, () => {
     const result = runJest('error-on-deprecated', [
       testFile,
@@ -42,9 +42,9 @@ testFiles.forEach(testFile => {
 
     expect(rest).toMatchSnapshot();
   });
-});
+}
 
-testFiles.forEach(testFile => {
+for (const testFile of testFiles) {
   const shouldPass = SHOULD_NOT_PASS_IN_JEST.has(testFile);
 
   const expectation = `${testFile} ${shouldPass ? 'errors' : 'passes'}`;
@@ -54,4 +54,4 @@ testFiles.forEach(testFile => {
     const result = runJest('error-on-deprecated', [testFile]);
     expect(result.exitCode).toBe(shouldPass ? 1 : 0);
   });
-});
+}

e2e/__tests__/snapshot.test.ts

@@ -70,19 +70,19 @@ const getSnapshotOfCopy = () => {
 
 describe('Snapshot', () => {
   const cleanup = () => {
-    [
+    for (const file of [
       snapshotFile,
       secondSnapshotFile,
       snapshotOfCopy,
       copyOfTestPath,
       snapshotEscapeFile,
       snapshotEscapeRegexFile,
       snapshotEscapeSubstitutionFile,
-    ].forEach(file => {
+    ]) {
       if (fileExists(file)) {
         fs.unlinkSync(file);
       }
-    });
+    }
     if (fileExists(snapshotDir)) {
       fs.rmdirSync(snapshotDir);
     }

e2e/__tests__/summaryThreshold.test.ts

@@ -7,7 +7,7 @@
 
 import runJest from '../runJest';
 
-['default', 'summary'].forEach(reporter => {
+for (const reporter of ['default', 'summary']) {
   describe(`${reporter} reporter`, () => {
     test('prints failure messages when total number of test suites is over summaryThreshold', () => {
       const {exitCode, stderr} = runJest('summary-threshold', [
@@ -26,4 +26,4 @@ import runJest from '../runJest';
       );
     });
   });
-});
+}

e2e/__tests__/transform.test.ts

@@ -199,9 +199,9 @@ describe('transformer caching', () => {
     const loggedFiles = stdout.split('\n');
 
     // Verify any lines logged are _just_ the file we care about
-    loggedFiles.forEach(line => {
+    for (const line of loggedFiles) {
       expect(line).toBe(transformedFile);
-    });
+    }
 
     // We run with 2 workers, so the file should be transformed twice
     expect(loggedFiles).toHaveLength(2);

e2e/__tests__/watchModeOnlyFailed.test.ts

@@ -41,9 +41,9 @@ test('can press "f" to run only failed tests', () => {
   const results = extractSummaries(stderr);
 
   expect(results).toHaveLength(2);
-  results.forEach(({rest, summary}) => {
+  for (const {rest, summary} of results) {
     expect(rest).toMatchSnapshot('test results');
     expect(summary).toMatchSnapshot('test summary');
-  });
+  }
   expect(exitCode).toBe(0);
 });

e2e/__tests__/watchModePatterns.test.ts

@@ -47,10 +47,10 @@ test('can press "p" to filter by file name', () => {
 
   expect(stdout).toMatchSnapshot();
   expect(results).toHaveLength(2);
-  results.forEach(({rest, summary}) => {
+  for (const {rest, summary} of results) {
     expect(rest).toMatchSnapshot('test results');
     expect(summary).toMatchSnapshot('test summary');
-  });
+  }
   expect(exitCode).toBe(0);
 });
 
@@ -66,9 +66,9 @@ test('can press "t" to filter by test name', () => {
 
   expect(stdout).toMatchSnapshot();
   expect(results).toHaveLength(2);
-  results.forEach(({rest, summary}) => {
+  for (const {rest, summary} of results) {
     expect(rest).toMatchSnapshot('test results');
     expect(summary).toMatchSnapshot('test summary');
-  });
+  }
   expect(exitCode).toBe(0);
 });

e2e/__tests__/watchModeUpdateSnapshot.test.ts

@@ -46,9 +46,9 @@ test('can press "u" to update snapshots', () => {
   const {exitCode, stderr} = runJest(DIR, ['--no-watchman', '--watchAll']);
   const results = extractSummaries(stderr);
   expect(results).toHaveLength(2);
-  results.forEach(({rest, summary}) => {
+  for (const {rest, summary} of results) {
     expect(rest).toMatchSnapshot('test results');
     expect(summary).toMatchSnapshot('test summary');
-  });
+  }
   expect(exitCode).toBe(0);
 });

e2e/custom-reporters/reporters/AssertionCountsReporter.js

@@ -9,13 +9,13 @@
 
 class AssertionCountsReporter {
   onTestFileResult(test, testResult, aggregatedResult) {
-    testResult.testResults.forEach((testCaseResult, index) => {
+    for (const [index, testCaseResult] of testResult.testResults.entries()) {
       console.log(
         `onTestFileResult testCaseResult ${index}: ${testCaseResult.title}, ` +
           `status: ${testCaseResult.status}, ` +
           `numExpectations: ${testCaseResult.numPassingAsserts}`,
       );
-    });
+    }
   }
   onTestCaseResult(test, testCaseResult) {
     console.log(

e2e/jasmine-async/__tests__/returningValues.test.js

@@ -8,7 +8,7 @@
 'use strict';
 
 describe('returning values', () => {
-  [
+  for (const val of [
     1,
     'string',
     0.1,
@@ -20,7 +20,7 @@ describe('returning values', () => {
     [1],
     {},
     () => {},
-  ].forEach(val => {
+  ]) {
     it(`throws if '${val}:${typeof val}' is returned`, () => val);
-  });
+  }
 });

packages/diff-sequences/__benchmarks__/test.js

@@ -142,13 +142,13 @@ const testLength = n => {
 
   writeHeading3(n);
 
-  [2, 4, 8].forEach(tenth => {
+  for (const tenth of [2, 4, 8]) {
     testDeleteInsert(
       tenth,
       all,
       getItems(n, i => i % 10 >= tenth && `${i}`),
     );
-  });
+  }
   testChange(
     1,
     all,

packages/expect-utils/src/__tests__/utils.test.ts

@@ -118,7 +118,7 @@ describe('getPath()', () => {
 });
 
 describe('getObjectSubset', () => {
-  [
+  for (const [object, subset, expected] of [
     [{a: 'b', c: 'd'}, {a: 'd'}, {a: 'b'}],
     [{a: [1, 2], b: 'b'}, {a: [3, 4]}, {a: [1, 2]}],
     [[{a: 'b', c: 'd'}], [{a: 'z'}], [{a: 'b'}]],
@@ -129,15 +129,15 @@ describe('getObjectSubset', () => {
     ],
     [{a: [1]}, {a: [1, 2]}, {a: [1]}],
     [new Date('2015-11-30'), new Date('2016-12-30'), new Date('2015-11-30')],
-  ].forEach(([object, subset, expected]) => {
+  ]) {
     test(
       `expect(getObjectSubset(${stringify(object)}, ${stringify(subset)}))` +
         `.toEqual(${stringify(expected)})`,
       () => {
         expect(getObjectSubset(object, subset)).toEqual(expected);
       },
     );
-  });
+  }
 
   describe('returns the object instance if the subset has no extra properties', () => {
     test('Date', () => {

packages/expect-utils/src/utils.ts

@@ -140,18 +140,18 @@ export const getObjectSubset = (
     const trimmed: any = {};
     seenReferences.set(object, trimmed);
 
-    getObjectKeys(object)
-      .filter(key => hasPropertyInObject(subset, key))
-      .forEach(key => {
-        trimmed[key] = seenReferences.has(object[key])
-          ? seenReferences.get(object[key])
-          : getObjectSubset(
-              object[key],
-              subset[key],
-              customTesters,
-              seenReferences,
-            );
-      });
+    for (const key of getObjectKeys(object).filter(key =>
+      hasPropertyInObject(subset, key),
+    )) {
+      trimmed[key] = seenReferences.has(object[key])
+        ? seenReferences.get(object[key])
+        : getObjectSubset(
+            object[key],
+            subset[key],
+            customTesters,
+            seenReferences,
+          );
+    }
 
     if (getObjectKeys(trimmed).length > 0) {
       return trimmed;
@@ -440,7 +440,7 @@ export const partition = <T>(
 ): [Array<T>, Array<T>] => {
   const result: [Array<T>, Array<T>] = [[], []];
 
-  items.forEach(item => result[predicate(item) ? 0 : 1].push(item));
+  for (const item of items) result[predicate(item) ? 0 : 1].push(item);
 
   return result;
 };