Add a test.

integration_tests/snapshot-serializers/package.json

@@ -1,6 +1,9 @@
 {
   "jest": {
     "testEnvironment": "node",
+    "transform": {
+      "^.+\\.js$": "<rootDir>/transformer.js"
+    },
     "snapshotSerializers": [
       "./plugins/foo",
       "<rootDir>/plugins/bar"

integration_tests/snapshot-serializers/plugins/bar.js

@@ -8,5 +8,8 @@
  */
 'use strict';
 
+/* eslint-disable no-unused-vars */
+
 const createPlugin = require('../utils').createPlugin;
-module.exports = createPlugin('bar');
+
+// We inject the call to "createPlugin('bar') through the transformer"

integration_tests/snapshot-serializers/transformer.js

@@ -0,0 +1,18 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc. All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+'use strict';
+
+module.exports = {
+  process(src, filename, config, options) {
+    if (/plugins\/bar/.test(filename)) {
+      return `${src};\module.exports = createPlugin('bar');`;
+    }
+    return src;
+  },
+};

integration_tests/snapshot-serializers/utils.js

@@ -10,7 +10,7 @@
 
 exports.createPlugin = prop => {
   return {
-    print: (val, serialize) => `${prop}: ${serialize(val[prop])}`,
+    print: (val, serialize) => `${prop} - ${serialize(val[prop])}`,
     test: val => val && val.hasOwnProperty(prop),
   };
 };