From 0e8934e4a1466b13a801cf3f9de097cd9ecf4566 Mon Sep 17 00:00:00 2001
From: Daniel Schmidt <danielmschmidt92@gmail.com>
Date: Sat, 3 Mar 2018 12:41:25 +0100
Subject: [PATCH] Enable single thread mode for runner

Some runners for tools that can not be run in parallel need a way
to specify that they should not be executed in parallel. This commits
adds this functionality.

Closes #5706
---
 CHANGELOG.md                                  |  3 +
 docs/Configuration.md                         |  4 ++
 .../src/__tests__/test_scheduler.test.js      | 57 +++++++++++++++++++
 packages/jest-cli/src/test_scheduler.js       |  2 +-
 4 files changed, 65 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 79bf4ef86472..fd78c73d1236 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,9 @@
   ([#5670](https://github.com/facebook/jest/pull/5670))
 * `[expect]` Add inverse matchers (`expect.not.arrayContaining`, etc.,
   [#5517](https://github.com/facebook/jest/pull/5517))
+* `[jest-cli]` Add `isSerial` property that runners can expose to specify that
+  they can not run in parallel
+  [#5706](https://github.com/facebook/jest/pull/5706)
 
 ### Fixes
 
diff --git a/docs/Configuration.md b/docs/Configuration.md
index dc70b54fd4f6..0629190f3f9f 100644
--- a/docs/Configuration.md
+++ b/docs/Configuration.md
@@ -703,6 +703,10 @@ async runTests(
 ): Promise<void>
 ```
 
+If you need to restrict your test-runner to only run in serial rather then being
+executed in parallel your class should have the property `isSerial` to be
+set as `true`.
+
 ### `setupFiles` [array]
 
 Default: `[]`
diff --git a/packages/jest-cli/src/__tests__/test_scheduler.test.js b/packages/jest-cli/src/__tests__/test_scheduler.test.js
index 352e62a62771..25a43f02aad2 100644
--- a/packages/jest-cli/src/__tests__/test_scheduler.test.js
+++ b/packages/jest-cli/src/__tests__/test_scheduler.test.js
@@ -12,6 +12,20 @@ import TestScheduler from '../test_scheduler';
 import SummaryReporter from '../reporters/summary_reporter';
 
 jest.mock('../reporters/default_reporter');
+const mockSerialRunner = {
+  isSerial: true,
+  runTests: jest.fn(),
+};
+jest.mock('jest-runner-serial', () => jest.fn(() => mockSerialRunner), {
+  virtual: true,
+});
+
+const mockParallelRunner = {
+  runTests: jest.fn(),
+};
+jest.mock('jest-runner-parallel', () => jest.fn(() => mockParallelRunner), {
+  virtual: true,
+});
 
 test('.addReporter() .removeReporter()', () => {
   const scheduler = new TestScheduler({}, {});
@@ -21,3 +35,46 @@ test('.addReporter() .removeReporter()', () => {
   scheduler.removeReporter(SummaryReporter);
   expect(scheduler._dispatcher._reporters).not.toContain(reporter);
 });
+
+test('schedule tests run in parallel per default', async () => {
+  const scheduler = new TestScheduler({}, {});
+  const test = {
+    context: {
+      config: {
+        runner: 'jest-runner-parallel',
+      },
+    },
+    path: './test/path.js',
+  };
+  const tests = [test, test];
+  try {
+    await scheduler.scheduleTests(tests);
+  } catch (e) {
+    // Fails because a haste map is needed, irrelevant for the test
+  }
+
+  expect(mockParallelRunner.runTests).toHaveBeenCalled();
+  expect(mockParallelRunner.runTests.mock.calls[0][5].serial).toBeFalsy();
+});
+
+test('schedule tests run in serial if the runner flags them', async () => {
+  const scheduler = new TestScheduler({}, {});
+  const test = {
+    context: {
+      config: {
+        runner: 'jest-runner-serial',
+      },
+    },
+    path: './test/path.js',
+  };
+
+  const tests = [test, test];
+  try {
+    await scheduler.scheduleTests(tests);
+  } catch (e) {
+    // Fails because a haste map is needed, irrelevant for the test
+  }
+
+  expect(mockSerialRunner.runTests).toHaveBeenCalled();
+  expect(mockSerialRunner.runTests.mock.calls[0][5].serial).toBeTruthy();
+});
diff --git a/packages/jest-cli/src/test_scheduler.js b/packages/jest-cli/src/test_scheduler.js
index 2f7ec55002c0..3d5fb7d18064 100644
--- a/packages/jest-cli/src/test_scheduler.js
+++ b/packages/jest-cli/src/test_scheduler.js
@@ -192,7 +192,7 @@ export default class TestScheduler {
             onResult,
             onFailure,
             {
-              serial: runInBand,
+              serial: runInBand || testRunners[runner].isSerial,
             },
           );
         }