Normalize --findRelatedTests paths on win32 platforms

CHANGELOG.md

@@ -13,6 +13,7 @@
 - `[jest-config]` Merge preset globals with project globals ([#9027](https://github.com/facebook/jest/pull/9027))
 - `[jest-config]` Support `.cjs` config files ([#9291](https://github.com/facebook/jest/pull/9291))
 - `[jest-core]` Support reporters as default exports ([#9161](https://github.com/facebook/jest/pull/9161))
+- `[jest-core]` Support `--findRelatedTests` paths case insensitivity on Windows ([#8900](https://github.com/facebook/jest/issues/8900))
 - `[jest-diff]` Add options for colors and symbols ([#8841](https://github.com/facebook/jest/pull/8841))
 - `[jest-diff]` [**BREAKING**] Export as ECMAScript module ([#8873](https://github.com/facebook/jest/pull/8873))
 - `[jest-diff]` Add `includeChangeCounts` and rename `Indicator` options ([#8881](https://github.com/facebook/jest/pull/8881))

e2e/__tests__/findRelatedFiles.test.ts

@@ -38,6 +38,32 @@ describe('--findRelatedTests flag', () => {
     expect(stderr).toMatch(summaryMsg);
   });
 
+  test('runs tests related to uppercased filename on case-insensitive os', () => {
+    if (process.platform !== 'win32') {
+      // This test is Windows specific, skip it on other platforms.
+      return;
+    }
+
+    writeFiles(DIR, {
+      '.watchmanconfig': '',
+      '__tests__/test.test.js': `
+      const a = require('../a');
+      test('a', () => {});
+    `,
+      'a.js': 'module.exports = {};',
+      'package.json': JSON.stringify({jest: {testEnvironment: 'node'}}),
+    });
+
+    const {stdout} = runJest(DIR, ['A.JS']);
+    expect(stdout).toMatch('');
+
+    const {stderr} = runJest(DIR, ['--findRelatedTests', 'A.JS']);
+    expect(stderr).toMatch('PASS __tests__/test.test.js');
+
+    const summaryMsg = 'Ran all test suites related to files matching /A.JS/i.';
+    expect(stderr).toMatch(summaryMsg);
+  });
+
   test('runs tests related to filename with a custom dependency extractor', () => {
     writeFiles(DIR, {
       '.watchmanconfig': '',

packages/jest-core/src/SearchSource.ts

@@ -5,6 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import * as os from 'os';
 import * as path from 'path';
 import micromatch = require('micromatch');
 import {Context} from 'jest-runtime';
@@ -252,8 +253,6 @@ export default class SearchSource {
     globalConfig: Config.GlobalConfig,
     changedFiles?: ChangedFiles,
   ): SearchResult {
-    const paths = globalConfig.nonFlagArgs;
-
     if (globalConfig.onlyChanged) {
       if (!changedFiles) {
         throw new Error('Changed files must be set when running with -o.');
@@ -263,7 +262,21 @@ export default class SearchSource {
         changedFiles,
         globalConfig.collectCoverage,
       );
-    } else if (globalConfig.runTestsByPath && paths && paths.length) {
+    }
+
+    let paths = globalConfig.nonFlagArgs;
+
+    if (globalConfig.findRelatedTests && 'win32' === os.platform()) {
+      const allFiles = this._context.hasteFS.getAllFiles();
+      const options = {nocase: true, windows: false};
+
+      paths = paths
+        .map(p => path.resolve(this._context.config.cwd, p))
+        .map(p => micromatch(allFiles, p.replace(/\\/g, '\\\\'), options)[0])
+        .filter(p => p);
+    }
+
+    if (globalConfig.runTestsByPath && paths && paths.length) {
       return this.findTestsByPaths(paths);
     } else if (globalConfig.findRelatedTests && paths && paths.length) {
       return this.findRelatedTestsFromPattern(