Improve documentation for testing web endpoints with `@SpringBootTest` and mock

[dsyer]

The user guide has a whole section on TestRestTemplate which is great. It doesn't help for a vanilla @SpringBootTest though because the default WebEnvironment is MOCK (I think). My understanding was that WebTestClient was usable wherever MockMvc would have been (i.e the default test environment). But you can't @Autowired one by default.

You have to explicitly @AutoConfigureWebTestClient. There is actually a side bar note about that, but it's quite hard to find, since it is in the section on @WebFluxTest, which I wasn't using.

[snicoll]

I think what's missing is a section with @SpringBootTest and testing endpoints in the default mode. Neither MockMvc nor WebTestClient seem to be very well documented.