Enable jest cacheDirectory configuration

packages/react-scripts/scripts/utils/createJestConfig.js

@@ -69,6 +69,7 @@ module.exports = (resolve, rootDir, isEjecting) => {
     'resetModules',
     'snapshotSerializers',
     'watchPathIgnorePatterns',
+    'cacheDirectory',
   ];
   if (overrides) {
     supportedKeys.forEach(key => {

packages/react-scripts/template/README.md

@@ -1539,6 +1539,10 @@ Supported overrides:
  - [`coverageReporters`](https://facebook.github.io/jest/docs/en/configuration.html#coveragereporters-array-string)
  - [`coverageThreshold`](https://facebook.github.io/jest/docs/en/configuration.html#coveragethreshold-object)
  - [`snapshotSerializers`](https://facebook.github.io/jest/docs/en/configuration.html#snapshotserializers-array-string)
+ - [`resetMocks`](https://facebook.github.io/jest/docs/en/configuration.html#resetmocks-boolean)
+ - [`resetModules`](https://facebook.github.io/jest/docs/en/configuration.html#resetmodules-boolean)
+ - [`watchPathIgnorePatterns`](https://facebook.github.io/jest/docs/en/configuration.html#watchpathignorepatterns-array-string)
+ - [`cacheDirectory`](https://facebook.github.io/jest/docs/en/configuration.html#watchpathignorepatterns-array-string)
 
 Example package.json:
 
@@ -1560,7 +1564,8 @@ Example package.json:
       }
     },
     "coverageReporters": ["text"],
-    "snapshotSerializers": ["my-serializer-module"]
+    "snapshotSerializers": ["my-serializer-module"],
+    "cacheDirectory": ".tmp/cache/jest"
   }
 }
 ```
@@ -1635,6 +1640,18 @@ The test command will force Jest to run tests once instead of launching the watc
 
 The build command will check for linter warnings and fail if any are found.
 
+### Speeding up CI tests with jest cache
+
+To speed up tests, Jest uses a cache. Unfortunately it saves the cache in hard-to-predict directory by default, making it difficult to save this cache in between builds on the CI environment. To counter this and make your tests run up to 2 times faster, you can specify which directory Jest should save it's cache to, by setting it in the `package.json`:
+
+```json
+  "jest": {
+    "cacheDirectory": ".tmp/cache/jest"
+  }
+```
+
+And then configuring your CI to cache that directory. See guides for [Travis CI](https://docs.travis-ci.com/user/caching/#Arbitrary-directories) and [CircleCI](https://circleci.com/docs/2.0/caching/) on how to configure cache directories.
+
 ### Disabling jsdom
 
 By default, the `package.json` of the generated project looks like this: