Mock Animated for testing

Summary:
Animated views can cause flakiness in snapshot tests. This mock replaces all provided Animated transforms with a blank animation.

This could potentially break some tests which animate in elements and then verify their existence. I can deal with that fallout in follow up diffs. One option is making all animations take 0 seconds when testing.

Reviewed By: cpojer

Differential Revision: D13811035

fbshipit-source-id: cc6b13c7d6bad29b125d35ef759a269bb0372e67

Author: Peter Argany

Libraries/Animated/src/Animated.js

@@ -10,7 +10,11 @@
 
 'use strict';
 
-const AnimatedImplementation = require('AnimatedImplementation');
+import Platform from 'Platform';
+
+const AnimatedImplementation = Platform.isTesting
+  ? require('AnimatedMock')
+  : require('AnimatedImplementation');
 
 module.exports = {
   get FlatList() {

Libraries/Animated/src/AnimatedImplementation.js

@@ -514,6 +514,8 @@ const event = function(argMapping: Array<?Mapping>, config?: EventConfig): any {
  * easy to build and maintain. `Animated` focuses on declarative relationships
  * between inputs and outputs, with configurable transforms in between, and
  * simple `start`/`stop` methods to control time-based animation execution.
+ * If additional transforms are added, be sure to include them in
+ * AnimatedMock.js as well.
  *
  * See http://facebook.github.io/react-native/docs/animated.html
  */

Libraries/Animated/src/AnimatedMock.js

@@ -0,0 +1,117 @@
+/**
+ * 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.
+ *
+ * @flow
+ * @format
+ */
+'use strict';
+
+const AnimatedImplementation = require('AnimatedImplementation');
+const AnimatedValueXY = require('./nodes/AnimatedValueXY');
+const AnimatedValue = require('./nodes/AnimatedValue');
+
+import type {EndCallback} from './animations/Animation';
+import type {TimingAnimationConfig} from './animations/TimingAnimation';
+import type {DecayAnimationConfig} from './animations/DecayAnimation';
+import type {SpringAnimationConfig} from './animations/SpringAnimation';
+import type {Mapping, EventConfig} from './AnimatedEvent';
+
+/**
+ * Animations are a source of flakiness in snapshot testing. This mock replaces
+ * animation functions from AnimatedImplementation with empty animations for
+ * predictability in tests.
+ */
+type CompositeAnimation = {
+  start: (callback?: ?EndCallback) => void,
+  stop: () => void,
+  reset: () => void,
+  _startNativeLoop: (iterations?: number) => void,
+  _isUsingNativeDriver: () => boolean,
+};
+
+const emptyAnimation = {
+  start: () => {},
+  stop: () => {},
+  reset: () => {},
+  _startNativeLoop: () => {},
+  _isUsingNativeDriver: () => {
+    return false;
+  },
+};
+
+const spring = function(
+  value: AnimatedValue | AnimatedValueXY,
+  config: SpringAnimationConfig,
+): CompositeAnimation {
+  return emptyAnimation;
+};
+
+const timing = function(
+  value: AnimatedValue | AnimatedValueXY,
+  config: TimingAnimationConfig,
+): CompositeAnimation {
+  return emptyAnimation;
+};
+
+const decay = function(
+  value: AnimatedValue | AnimatedValueXY,
+  config: DecayAnimationConfig,
+): CompositeAnimation {
+  return emptyAnimation;
+};
+
+const sequence = function(
+  animations: Array<CompositeAnimation>,
+): CompositeAnimation {
+  return emptyAnimation;
+};
+
+type ParallelConfig = {
+  stopTogether?: boolean,
+};
+const parallel = function(
+  animations: Array<CompositeAnimation>,
+  config?: ?ParallelConfig,
+): CompositeAnimation {
+  return emptyAnimation;
+};
+
+const delay = function(time: number): CompositeAnimation {
+  return emptyAnimation;
+};
+
+const stagger = function(
+  time: number,
+  animations: Array<CompositeAnimation>,
+): CompositeAnimation {
+  return emptyAnimation;
+};
+
+type LoopAnimationConfig = {iterations: number};
+
+const loop = function(
+  animation: CompositeAnimation,
+  {iterations = -1}: LoopAnimationConfig = {},
+): CompositeAnimation {
+  return emptyAnimation;
+};
+
+const event = function(argMapping: Array<?Mapping>, config?: EventConfig): any {
+  return null;
+};
+
+module.exports = {
+  ...AnimatedImplementation,
+  decay,
+  timing,
+  spring,
+  delay,
+  sequence,
+  parallel,
+  stagger,
+  loop,
+  event,
+};