Introduce TestRestTemplate Kotlin extensions

[sdeleuze]

This commit introduces Kotlin extensions similar to the RestOperations ones in order to be able to take advantage of Kotlin reified type parameters for example.

Fixes gh-8062

[snicoll]

Dependencies are (meant to be) ordered alphabetically. Can you please rework this?

[snicoll]

I am confused. In the spring-boot module you've set the maven compiler phases to none. Why isn't it necessary here?

[sdeleuze]

Good catch, it is, I will update the PR accordingly.

[sdeleuze]

@snicoll I have pushed an updated commit with your feedback taken in account.

[snicoll]

Thanks @sdeleuze. One more thing: we have a test that validates that our TestRestTemplate provides the same features as the original RestTemplate. Would it be possible to add a similar test to assert that this Kotlin extension is equivalent to the one for RestTemplate?

[sdeleuze]

@snicoll In Java, the test uses reflection to list all RestOperations methods and invoke their TestRestTemplate counterparts, but extensions are top level functions. Unless I miss something, I can see a reasonably complex way of doing the same kind of check with Kotlin extensions.

[wilkinsona]

@sdeleuze Perhaps we could do a similar but less extensive check? It would at least be nice to have a test that verifies that we have a top-level function for each method, even if the test doesn't invoke the function. I am working on the perhaps naive assumption that Kotlin is compiled to byte code so we must be able to introspect that byte code…

[sdeleuze]

@wilkinsona But we don't have 1 extension for each method, we only provide the relevant ones.

[wilkinsona]

Sorry, "each method" was a little imprecise. I should have written "each method that's relevant". Assuming that we can identify a relevant method programatically, my hope is that it would be possible to test that there's a corresponding top-level function for that method.

[sdeleuze]

@snicoll @wilkinsona I have been able to create such test using a mix of Java and Kotlin reflection. It allowed to find 5 missing extensions, thanks for pushing for this ;-) I have added the missing extensions to this PR and to Spring Framework 5.0.2 as well via SPR-16229. Can you please merge this commit in order to be included as part of 2.0.0.M7?

[snicoll]

Sébastien shared he'd like to use that feature during an upcoming workshop.