fix: Jest mutli-project-runner still cannot handle exactly one project

Add failing test case

Explicitly distinguish if project has been added using process.cwd

Fix CI errors

Add back old test

Apply solution without isGlobalProject

Apply suggestion from code review

Add changelog

CHANGELOG.md

@@ -40,6 +40,7 @@
 - `[expect]` Consider all RegExp flags for equality ([#9167](https://github.com/facebook/jest/pull/9167))
 - `[expect]` [**BREAKING**] Consider primitives different from wrappers instantiated with `new` ([#9167](https://github.com/facebook/jest/pull/9167))
 - `[jest-config]` Use half of the available cores when `watchAll` mode is enabled ([#9117](https://github.com/facebook/jest/pull/9117))
+- `[jest-config]` Fix Jest multi project runner still cannot handle exactly one project ([#8894](https://github.com/facebook/jest/pull/8894))
 - `[jest-console]` Add missing `console.group` calls to `NullConsole` ([#9024](https://github.com/facebook/jest/pull/9024))
 - `[jest-core]` Don't include unref'd timers in --detectOpenHandles results ([#8941](https://github.com/facebook/jest/pull/8941))
 - `[jest-diff]` Do not inverse format if line consists of one change ([#8903](https://github.com/facebook/jest/pull/8903))

e2e/__tests__/multiProjectRunner.test.ts

@@ -199,7 +199,57 @@ test.each([{projectPath: 'packages/somepackage'}, {projectPath: 'packages/*'}])(
     });
 
     const {stdout, stderr, exitCode} = runJest(DIR, ['--no-watchman']);
-    expect(stderr).toContain('PASS packages/somepackage/test.js');
+    expect(stderr).toContain('PASS somepackage packages/somepackage/test.js');
+    expect(stderr).toContain('Test Suites: 1 passed, 1 total');
+    expect(stdout).toEqual('');
+    expect(exitCode).toEqual(0);
+  },
+);
+
+test.each([
+  {displayName: 'p1', projectPath: 'packages/p1'},
+  {displayName: 'p2', projectPath: 'packages/p2'},
+])(
+  'correctly runs a single non-root project',
+  ({projectPath, displayName}: {projectPath: string; displayName: string}) => {
+    writeFiles(DIR, {
+      'package.json': `
+        {
+          "jest": {
+            "projects": [
+              "${projectPath}"
+            ]
+          }
+        }
+      `,
+      'packages/p1/package.json': `
+        {
+          "jest": {
+            "displayName": "p1"
+          }
+        }
+      `,
+      'packages/p1/test.js': `
+        test('1+1', () => {
+          expect(1).toBe(1);
+        });
+      `,
+      'packages/p2/package.json': `
+        {
+          "jest": {
+            "displayName": "p2"
+          }
+        }
+      `,
+      'packages/p2/test.js': `
+        test('1+1', () => {
+          expect(1).toBe(1);
+        });
+      `,
+    });
+
+    const {stdout, stderr, exitCode} = runJest(DIR, ['--no-watchman']);
+    expect(stderr).toContain(`PASS ${displayName} ${projectPath}/test.js`);
     expect(stderr).toContain('Test Suites: 1 passed, 1 total');
     expect(stdout).toEqual('');
     expect(exitCode).toEqual(0);

packages/jest-config/src/index.ts

@@ -9,6 +9,7 @@ import * as fs from 'fs';
 import * as path from 'path';
 import {Config} from '@jest/types';
 import chalk = require('chalk');
+import {sync as realpath} from 'realpath-native';
 import {isJSONString, replaceRootDirInPath} from './utils';
 import normalize from './normalize';
 import resolveConfigPath from './resolveConfigPath';
@@ -278,26 +279,24 @@ export function readConfigs(
     const parsedConfig = readConfig(argv, projects[0]);
     configPath = parsedConfig.configPath;
 
-    if (parsedConfig.globalConfig.projects) {
-      // If this was a single project, and its config has `projects`
-      // settings, use that value instead.
-      projects = parsedConfig.globalConfig.projects;
-    }
-
     hasDeprecationWarnings = parsedConfig.hasDeprecationWarnings;
     globalConfig = parsedConfig.globalConfig;
     configs = [parsedConfig.projectConfig];
     if (globalConfig.projects && globalConfig.projects.length) {
       // Even though we had one project in CLI args, there might be more
       // projects defined in the config.
+      // In other words, if this was a single project,
+      // and its config has `projects` settings, use that value instead.
       projects = globalConfig.projects;
     }
   }
 
-  if (
-    projects.length > 1 ||
-    (projects.length && typeof projects[0] === 'object')
-  ) {
+  if (projects.length > 0) {
+    const projectIsCwd =
+      process.platform === 'win32'
+        ? projects[0] === realpath(process.cwd())
+        : projects[0] === process.cwd();
+
     const parsedConfigs = projects
       .filter(root => {
         // Ignore globbed files that cannot be `require`d.
@@ -313,9 +312,19 @@ export function readConfigs(
 
         return true;
       })
-      .map((root, projectIndex) =>
-        readConfig(argv, root, true, configPath, projectIndex),
-      );
+      .map((root, projectIndex) => {
+        const projectIsTheOnlyProject =
+          projectIndex === 0 && projects.length === 1;
+        const skipArgvConfigOption = !(projectIsTheOnlyProject && projectIsCwd);
+
+        return readConfig(
+          argv,
+          root,
+          skipArgvConfigOption,
+          configPath,
+          projectIndex,
+        );
+      });
 
     ensureNoDuplicateConfigs(parsedConfigs, projects);
     configs = parsedConfigs.map(({projectConfig}) => projectConfig);