Add test that generated invalid code

[Meijuh]

This PR adds a unit test assertThrowsAssignment that generates invalid code. In JUnit assertThrows returns the exception that is thrown, while in AssertJ there is no way (currently) to obtain the exception that is thrown.

The purpose of this PR is check whether it is desired behavior open rewrite generates invalid Java code. A solution would be to skip rewriting cases where assertThrows is used as RHS in an assignment, but that would leave JUnit assertions in code bases.

[timtebeek]

Thanks for adding a test to reproduce an issue! Indeed best to not convert such cases if there's no direct replacement in AssertJ. If you add @ExpectedToFail we can already merge your PR as is; or if you'd like to attempt to fix the issue too, you're more than welcome to have a go. Whatever you prefer.

[Meijuh]

I'll push a fix that leaves such a case as is. Shouldn't be too hard to check if the assertThrows appears on the RHS of an assignment.

[Meijuh]

Instead of blacklisting the case where assertThrows appears on the RHS of an assignment, I decided to whitelist the case where assertThrows appears immediately inside a J.Block. This is to ensure the degenerate test case I added (and more like it) would not fail.

Also, I am unsure what exactly the code style is, where can I find it? Is the style I used okay?

[timtebeek]

Instead of blacklisting the case where assertThrows appears on the RHS of an assignment, I decided to whitelist the case where assertThrows appears immediately inside a J.Block. This is to ensure the degenerate test case I added (and more like it) would not fail.

Looks like a fine addition to me; thanks for taking the time to think through other limitations as well, and providing a fix.

Also, I am unsure what exactly the code style is, where can I find it? Is the style I used okay?

We typically use the IntelliJ default, sometimes supplemented with .editorconfig.

I like the changes you've made! My only change is adding the Issue annotation with links here, such that we can refer to this discussion.

[timtebeek]

Thanks a lot! While we wait for the for the next release in a week or two you can already use our snapshot versions.