`assertThat(boolean)` is harmful - violates fluent API principles

This was raised before by @cpovirk https://github.com/google/truth/issues/48 and IMO the suggestion that error prone would catch it is irrelevant since truth doesn’t require error prone.

Truth is a fluent API so the “contract” is that grammatically correct things would work as expected: “assert that something is true” is correct, yet Truth requires a double boolean check.

This looks natural:

assertThat(e.getStatus().getCode() == Status.ALREADY_EXISTS.getCode());

It’s also consistent with how Guava preconditions work, however it’s wrong and will always pass.

The correct (boolean) version is not fluent

assertThat(e.getStatus().getCode() == Status.ALREADY_EXISTS.getCode()).isTrue();

// and yes, it should be

assertThat(e.getStatus().getCode()).isEqualTo(Status.ALREADY_EXISTS.getCode());

Worse it’s terribly difficult to spot and that’s a sign of a bad API.

[cpovirk]

This is quite possibly the biggest footgun in the Truth API. We once batted around some crazy ideas to try to catch it at runtime, but we couldn’t find anything that seemed like an improvement. At this point, we’re committed to the existing API. We might want to recommend Error Prone or similar static analysis somewhere prominent.

[jbduncan]

…for some reason I hadn’t seen the .isTrue() at the end of your first example, so sorry for missing that!