[jest] Capture and restore global promise

Author: mikeduminy

jest/preset.js

@@ -0,0 +1,9 @@
+const reactNativePreset = require('react-native/jest-preset');
+
+module.exports = Object.assign({}, reactNativePreset, {
+  // this is needed to make modern fake timers work
+  // because the react-native preset overrides global.Promise
+  setupFiles: [require.resolve('./save-promise.js')]
+    .concat(reactNativePreset.setupFiles)
+    .concat([require.resolve('./restore-promise.js')]),
+});

jest/restore-promise.js

@@ -0,0 +1 @@
+global.Promise = global.originalPromise;

jest/save-promise.js

@@ -0,0 +1 @@
+global.originalPromise = Promise;

package.json

@@ -70,7 +70,7 @@
     "build": "rm -rf build; babel src --out-dir build --ignore 'src/__tests__/*'"
   },
   "jest": {
-    "preset": "react-native",
+    "preset": "../jest/preset.js",
     "moduleFileExtensions": [
       "js",
       "json"