Turn on cleaning up of globals.

It will be come default in future jest release, currently jest isn't
emitting any warning so there is no reason to wait to turn it on.

jest.config.js

@@ -138,7 +138,10 @@ module.exports = {
   // testEnvironment: "jest-environment-node",
 
   // Options that will be passed to the testEnvironment
-  // testEnvironmentOptions: {},
+  // this will become default in future jest release
+  testEnvironmentOptions: {
+    globalsCleanup: "on",
+  },
 
   // Adds a location field to test results
   // testLocationInResults: false,