react-native: make automated fs-based tests platform-independent

Summary:
@public

These tests are using a mock memory FS to start with, so there is no reason at all they should depend on the host OS or filesystem details. This changeset fixes that so that we fully mock the `fs` and `path` modules dependending on the mock platform (not the host platform). I also added an example of how we can test both platforms (regardless of the host platform) in `findPackageClassName`. Follow up changeset will be to do the same for all the other affected tests.

Related to facebook/react-native#20260.

Reviewed By: mjesun

Differential Revision: D9771024

fbshipit-source-id: b368b43e8e54292d33b6183eec9a9ea69f2e6e76

__mocks__/fs.js

@@ -9,18 +9,21 @@
 
 'use strict';
 
-const fs = new (require('metro-memory-fs'))({cwd: process.cwd});
+const path = require('path');
+const MemoryFS = require('metro-memory-fs');
+let fs;
 
-function setMockFilesystem(object) {
-  fs.reset();
-  const root = process.platform === 'win32' ? 'c:\\' : '/';
+function setMockFilesystem(object, platform) {
+  reset(platform);
+  const root = platform === 'win32' ? 'c:\\' : '/';
   mockDir(root, {...object});
+  return root;
 }
 
 function mockDir(dirPath, desc) {
   for (const entName in desc) {
     const ent = desc[entName];
-    const entPath = require('path').join(dirPath, entName);
+    const entPath = path.join(dirPath, entName);
     if (typeof ent === 'string' || ent instanceof Buffer) {
       fs.writeFileSync(entPath, ent);
       continue;
@@ -37,7 +40,22 @@ function mockDir(dirPath, desc) {
   }
 }
 
-fs.__setMockFilesystem = setMockFilesystem;
-fs.mock = {clear: () => fs.reset()};
+function reset(platform) {
+  if (path.mock == null) {
+    throw new Error(
+      'to use this "fs" module mock, you must also mock the "path" module',
+    );
+  }
+  path.mock.reset(platform);
+  const cwd = () => (platform === 'win32' ? 'c:\\' : '/');
+  fs = new MemoryFS({platform, cwd});
+  Object.assign(mockFs, fs);
+}
+
+const mockFs = {};
+mockFs.__setMockFilesystem = setMockFilesystem;
+mockFs.mock = {clear: reset};
+
+reset('posix');
 
-module.exports = fs;
+module.exports = mockFs;

__mocks__/path.js

@@ -0,0 +1,20 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+'use strict';
+
+const mockPath = {};
+
+function reset(platform) {
+  Object.assign(mockPath, jest.requireActual('path')[platform]);
+}
+
+mockPath.mock = {reset};
+
+module.exports = mockPath;

core/__fixtures__/android.js

@@ -1,7 +1,14 @@
-/** @format */
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
 
 const fs = require.requireActual('fs');
-const path = require('path');
+const path = require.requireActual('path');
 
 const manifest = fs.readFileSync(
   path.join(__dirname, './files/AndroidManifest.xml'),

core/__tests__/android/findAndroidAppFolder.spec.js

@@ -10,6 +10,7 @@
 
 'use strict';
 
+jest.mock('path');
 jest.mock('fs');
 
 const fs = require('fs');

core/__tests__/android/findManifest.spec.js

@@ -10,6 +10,7 @@
 
 'use strict';
 
+jest.mock('path');
 jest.mock('fs');
 
 const findManifest = require('../../android/findManifest');

core/__tests__/android/findPackageClassName.spec.js

@@ -10,40 +10,49 @@
 
 'use strict';
 
+jest.mock('path');
 jest.mock('fs');
 
+const mocks = require('../../__fixtures__/android');
 const findPackageClassName = require('../../android/findPackageClassName');
 const fs = require('fs');
-const mocks = require('../../__fixtures__/android');
 
-describe('android::findPackageClassName', () => {
-  beforeAll(() => {
-    fs.__setMockFilesystem({
-      empty: {},
-      flatJava: {
-        android: mocks.valid,
-      },
-      flatKotlin: {
-        android: mocks.validKotlin,
-      },
+['posix', 'win32'].forEach(platform => {
+  let root;
+  describe(`android::findPackageClassName (${platform})`, () => {
+    beforeAll(() => {
+      root = fs.__setMockFilesystem(
+        {
+          empty: {},
+          flatJava: {
+            android: mocks.valid,
+          },
+          flatKotlin: {
+            android: mocks.validKotlin,
+          },
+        },
+        platform,
+      );
     });
-  });
 
-  it('returns manifest content if file exists in the folder', () => {
-    expect(typeof findPackageClassName('/flatJava')).toBe('string');
-  });
+    it('returns manifest content if file exists in the folder', () => {
+      expect(typeof findPackageClassName(root + 'flatJava')).toBe('string');
+    });
 
-  it('returns the name of the java class implementing ReactPackage', () => {
-    expect(findPackageClassName('/flatJava')).toBe('SomeExampleJavaPackage');
-  });
+    it('returns the name of the java class implementing ReactPackage', () => {
+      expect(findPackageClassName(root + 'flatJava')).toBe(
+        'SomeExampleJavaPackage',
+      );
+    });
 
-  it('returns the name of the kotlin class implementing ReactPackage', () => {
-    expect(findPackageClassName('/flatKotlin')).toBe(
-      'SomeExampleKotlinPackage',
-    );
-  });
+    it('returns the name of the kotlin class implementing ReactPackage', () => {
+      expect(findPackageClassName(root + 'flatKotlin')).toBe(
+        'SomeExampleKotlinPackage',
+      );
+    });
 
-  it('returns `null` if there are no matches', () => {
-    expect(findPackageClassName('/empty')).toBeNull();
+    it('returns `null` if there are no matches', () => {
+      expect(findPackageClassName(root + 'empty')).toBeNull();
+    });
   });
 });

core/__tests__/android/getDependencyConfig.spec.js

@@ -10,6 +10,7 @@
 
 'use strict';
 
+jest.mock('path');
 jest.mock('fs');
 
 const getDependencyConfig = require('../../android').dependencyConfig;

core/__tests__/android/getProjectConfig.spec.js

@@ -10,6 +10,7 @@
 
 'use strict';
 
+jest.mock('path');
 jest.mock('fs');
 
 const getProjectConfig = require('../../android').projectConfig;

core/__tests__/android/readManifest.spec.js

@@ -10,6 +10,7 @@
 
 'use strict';
 
+jest.mock('path');
 jest.mock('fs');
 
 const findManifest = require('../../android/findManifest');

core/__tests__/findAssets.spec.js

@@ -10,6 +10,7 @@
 
 'use strict';
 
+jest.mock('path');
 jest.mock('fs');
 
 const findAssets = require('../findAssets');

core/__tests__/ios/findPodfilePath.spec.js

@@ -10,6 +10,7 @@
 
 'use strict';
 
+jest.mock('path');
 jest.mock('fs');
 
 const findPodfilePath = require('../../ios/findPodfilePath');

core/__tests__/ios/findPodspecName.spec.js

@@ -10,6 +10,7 @@
 
 'use strict';
 
+jest.mock('path');
 jest.mock('fs');
 
 const findPodspecName = require('../../ios/findPodspecName');

core/__tests__/ios/findProject.spec.js

@@ -10,6 +10,7 @@
 
 'use strict';
 
+jest.mock('path');
 jest.mock('fs');
 
 const findProject = require('../../ios/findProject');

core/__tests__/ios/getProjectConfig.spec.js

@@ -10,6 +10,7 @@
 
 'use strict';
 
+jest.mock('path');
 jest.mock('fs');
 
 const getProjectConfig = require('../../ios').projectConfig;

link/__tests__/ios/writePlist.spec.js

@@ -10,6 +10,7 @@
 
 'use strict';
 
+jest.mock('path');
 jest.mock('fs');
 
 let plistPath = null;

util/__tests__/findSymlinkedModules-test.js

@@ -8,6 +8,7 @@
  * @emails oncall+javascript_foundation
  */
 
+jest.mock('path');
 jest.mock('fs');
 
 const fs = require('fs');