Add transform for stubbing electron

Summary:
The idea behind this is to enable tests running in pure node, without electron, because electron requires display drivers and complicated things.

I've been lazy and only added the bare minimum electron api's for the connection test to pass.
It would be awesome to auto generate it properly.

Reviewed By: danielbuechele

Differential Revision: D10238132

fbshipit-source-id: d4a2da2baf5f8964184b532a581c3a75ee33ef06

static/electron-stubs.notjs

@@ -0,0 +1,12 @@
+{
+  remote: {
+    process: {
+      env: {},
+    },
+    getCurrentWindow: function() {
+      return {
+        isFocused: function() {return true;}
+      };
+    },
+  },
+}

static/transforms/electron-stubs.js

@@ -0,0 +1,33 @@
+/**
+ * Copyright 2018-present Facebook.
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ * @format
+ */
+
+var babylon = require('@babel/parser');
+var fs = require('fs');
+
+var electronStubs = babylon.parseExpression(
+  fs.readFileSync('static/electron-stubs.notjs').toString(),
+);
+
+module.exports = function(babel) {
+  return {
+    name: 'replace-electron-requires-with-stubs',
+    visitor: {
+      CallExpression(path) {
+        if (
+          path.node.type === 'CallExpression' &&
+          path.node.callee.type === 'Identifier' &&
+          path.node.callee.name === 'require' &&
+          path.node.arguments.length > 0
+        ) {
+          if (path.node.arguments[0].value === 'electron') {
+            path.replaceWith(electronStubs);
+          }
+        }
+      },
+    },
+  };
+};

static/transforms/index.js

@@ -37,7 +37,11 @@ function transform({filename, options, src}) {
     require('./dynamic-requires.js'),
   ];
 
-  if (!options.isTestRunner) {
+  if (options.isTestRunner) {
+    if (process.env.USE_ELECTRON_STUBS) {
+      plugins.push(require('./electron-stubs.js'));
+    }
+  } else {
     // Replacing require statements with electronRequire to prevent metro from
     // resolving them. electronRequire are resolved during runtime by electron.
     // As the tests are not bundled by metro and run in @jest-runner/electron,