heyimalex · September 21, 2016 16:15 · Sep 21, 2016
diff --git a/example.js b/example.js
@@ -0,0 +1,24 @@
+// __tests__/example.js
+jest.mock('fs');
+
+it('should serve as a nice example', () => {
+
+  const fs = require('fs')
+
+  // fs can be set up at any point by calling __configureFs.
+  fs.__configureFs({
+    '/test': {
+      'a.foo': '----',
+
+      // mock-fs' other exports are also available on the fs object.
+      'b.bar': fs.__mockFile({
+        content: 'file content here',
+        ctime: new Date(1),
+        mtime: new Date(1)
+      }),
+  })
+
+  const results = fs.readdirSync('/test')
+  expect(results.length).toBe(2)
+  expect(results).toEqual(['a.foo', 'b.bar'])
+})
diff --git a/fs.js b/fs.js
@@ -0,0 +1,27 @@
+// __mocks__/fs.js
+const mockfs = require('mock-fs');
+
+const container = {
+  __internalFs: null,
+  __configureFs: (conf) => {
+    container.__internalFs = mockfs.fs(conf);
+  },
+  __mockFile: mockfs.file,
+  __mockDirectory: mockfs.directory,
+  __mockSymlink: mockfs.symlink,
+}
+
+const proxyfs = new Proxy(container, {
+  get: function (target, property, receiver) {
+    if (target.hasOwnProperty(property)) {
+      return target[property];
+    } else {
+      if (target.__internalFs === null) {
+        target.__internalFs = mockfs.fs();
+      }
+      return target.__internalFs[property];
+    }
+  }
+})
+
+module.exports = proxyfs;
diff --git a/jestsetup.js b/jestsetup.js
@@ -0,0 +1,7 @@
+// mock-fs hooks the native fs on first require, so unfortunately just using
+// the __mocks__ file isn't enough; jest will mock fs itself and stuff gets
+// complicated. I'm actually not completely sure _what_ happens, but the end
+// result is that you need to require mock fs before anything else or it
+// doesn't work.
+
+require('mock-fs')
diff --git a/package.json b/package.json
@@ -0,0 +1,12 @@
+{
+  "devDependencies": {
+    "jest": "^15.1.1",
+    "mock-fs": "^3.11.0",
+  },
+  "scripts": {
+    "test": "jest"
+  },
+  "jest": {
+    "setupFiles": ["<rootDir>/jestsetup.js"]
+  }
+}