Add assertThatCode(Callable) - #2519

LGTM :)

I think we can drop my attempt https://github.com/assertj/assertj-core/pull/2516/files

Slightly off topic, I think the existing assertThatCode is not great as it exposes throwable assertions, even if the code throws one, it does not read very nicely:

// why would we expect to have an exception here?
assertThatCode(() -> doStuff()).hasMessage("Boom!");

your version with callable is much better in that sense.
The existing alternative is:

// reads nicely
assertThatThrownBy(() -> doStuff()).hasMessage("Boom!");

Ideally I would replace the existing assertThatCode(ThrowingCallable) by your version but that's probably something we should do for AssertJ 4 as it's a might be too big of a breaking change (not sure how to evaluate this). What we could do though is deprecate assertThatCode(ThrowingCallable) in favor of assertThatThrownBy or assertThatCode(Callable).

Slightly off topic, I think the existing assertThatCode is not great as it exposes throwable assertions, even if the code throws one, it does not read very nicely

Yes, I tried to say that but with wrong wording 😆

I'm exploring the direction of ThrowingAssert for assertThatCode(Callable) and maybe it's not so pricey to introduce ThrowingRunnable and the corresponding assertThatCode as an alternative for assertThatCode(ThrowingCallable).

@joel-costigliola I went with ThrowingExecutableAssert, maybe clearer than just ThrowingAssert and harder to be confused with ThrowableAssert. Could you have a look and let me know what you think?

I'd experiment the replacement of assertThatCode(ThrowingCallable) in a separate PR/branch once this one is stable. I have the feeling it would be a binary incompatible change but source compatible at the same time, as long as no one used weird patterns like assertThatCode(...).hasMessage(...).

With the new assertion hierarchy (ThrowingExecutableAssert / AbstractThrowingExecutableAssert), a new assumeThatCode(Callable) cannot be easily added as all the code around Byte Buddy supports only AbstractAssert types.

We might add it in a second round, keeping only assumeThatCode(ThrowingRunnable) for the time being.