Catching lambda doesn't output the excpetion's message

If I assert expectThat(catching { ... }).isNull(), and it throws, it doesn’t print the exception’s message…

In my case:

▼ Expect that com.squareup.moshi.JsonDataException:
  ✗ is null

which doesn’t help too much to identify the source of the problem.

As a plus, it would be nice to have expectDoesNotThrow { }, that would allow to add more checks on a valid result.

[robfletcher]

Fixed with new expectCatching … failed construct (or existing expectThrows).

[robfletcher]

I’m working on something at the moment that does away with catching altogether. Kotlin already has the runCatching method. Instead of dealing with an exception or null we can use runCatching to produce a Result<T> that is either the value (as returned by the lambda) or the exception it threw. I think this makes much more sense for asserting against.

e.g.

expectCatching { ... }
  .failed()
  .isA<IllegalStateException>()

or

expectCatching { ... }
  .succeeded()
  .isEqualTo(...)

The existing expectThrows becomes a shorthand for the first form.

See #169