remove clever example in testing guide (#6903)
remove clever example in testing guide (#6903)

* remove clever example in testing guide

The creation of a custom navigation-specific testing harness seems a bit too purpose-built for most people. Change to an integration test that leverage JSDOM's browser globals to use BrowserRouter directly.

* add dom assertion at end of example

* fix for jsdom only supporting navigation via history api

* add link to RR page on RTL docs

* change to createMemoryHistory instead of browserrouter

* emphasize memoryrouter over alternatives in tests

ReactTraining/react-router,reactjs/react-router,rackt/react-router,ReactTraining/react-router,ReactTraining/react-router,ReactTraining/react-router,reactjs/react-router,rackt/react-router