fix: allow json file as manual mock

CHANGELOG.md

@@ -9,6 +9,7 @@
 - `[jest-changed-files]` Change method of obtaining git root ([#8052](https://github.com/facebook/jest/pull/8052))
 - `[jest-each]` Fix test function type ([#8145](https://github.com/facebook/jest/pull/8145))
 - `[jest-fake-timers]` `getTimerCount` not taking immediates and ticks into account ([#8139](https://github.com/facebook/jest/pull/8139))
+- `[jest-runtime]` Allow json file as manual mock ([#8159](https://github.com/facebook/jest/pull/8159))
 - `[pretty-format]` Print `BigInt` as a readable number instead of `{}` ([#8138](https://github.com/facebook/jest/pull/8138))
 
 ### Chore & Maintenance

e2e/mock-json/__mocks__/data.json

@@ -0,0 +1,3 @@
+{
+  "foo": "bar"
+}

e2e/mock-json/__tests__/index.js

@@ -0,0 +1,18 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+'use strict';
+
+jest.mock('../data.json');
+
+const extractData = require('../');
+
+describe('extractData', () => {
+  it('should read the data', () => {
+    expect(extractData()).toEqual(['foo']);
+  });
+});

e2e/mock-json/data.json

@@ -0,0 +1,3 @@
+{
+  "real": "data"
+}

e2e/mock-json/index.js

@@ -0,0 +1,14 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+const data = require('./data.json');
+
+function extractData() {
+  return Object.keys(data);
+}
+
+module.exports = extractData;

e2e/mock-json/package.json

@@ -0,0 +1,5 @@
+{
+  "jest": {
+    "testEnvironment": "node"
+  }
+}

packages/jest-runtime/src/index.ts

@@ -341,19 +341,15 @@ class Runtime {
         loaded: false,
       };
       moduleRegistry[modulePath] = localModule;
-      if (path.extname(modulePath) === '.json') {
-        localModule.exports = this._environment.global.JSON.parse(
-          stripBOM(fs.readFileSync(modulePath, 'utf8')),
-        );
-      } else if (path.extname(modulePath) === '.node') {
-        localModule.exports = require(modulePath);
-      } else {
-        // Only include the fromPath if a moduleName is given. Else treat as root.
-        const fromPath = moduleName ? from : null;
-        this._execModule(localModule, options, moduleRegistry, fromPath);
-      }
 
-      localModule.loaded = true;
+      this._loadModule(
+        localModule,
+        from,
+        moduleName,
+        modulePath,
+        options,
+        moduleRegistry,
+      );
     }
     return moduleRegistry[modulePath].exports;
   }
@@ -430,11 +426,16 @@ class Runtime {
         loaded: false,
       };
 
-      // Only include the fromPath if a moduleName is given. Else treat as root.
-      const fromPath = moduleName ? from : null;
-      this._execModule(localModule, undefined, mockRegistry, fromPath);
+      this._loadModule(
+        localModule,
+        from,
+        moduleName,
+        modulePath,
+        undefined,
+        mockRegistry,
+      );
+
       mockRegistry[moduleID] = localModule.exports;
-      localModule.loaded = true;
     } else {
       // Look for a real module to generate an automock from
       mockRegistry[moduleID] = this._generateMock(from, moduleName);
@@ -443,6 +444,28 @@ class Runtime {
     return mockRegistry[moduleID];
   }
 
+  private _loadModule(
+    localModule: InitialModule,
+    from: Config.Path,
+    moduleName: string | undefined,
+    modulePath: Config.Path,
+    options: InternalModuleOptions | undefined,
+    moduleRegistry: ModuleRegistry,
+  ) {
+    if (path.extname(modulePath) === '.json') {
+      localModule.exports = this._environment.global.JSON.parse(
+        stripBOM(fs.readFileSync(modulePath, 'utf8')),
+      );
+    } else if (path.extname(modulePath) === '.node') {
+      localModule.exports = require(modulePath);
+    } else {
+      // Only include the fromPath if a moduleName is given. Else treat as root.
+      const fromPath = moduleName ? from : null;
+      this._execModule(localModule, options, moduleRegistry, fromPath);
+    }
+    localModule.loaded = true;
+  }
+
   requireModuleOrMock(from: Config.Path, moduleName: string) {
     try {
       if (this._shouldMock(from, moduleName)) {