Assertions made inside the implementation of another Truth assertion should use check, not assertThat.

Before:

class MyProtoSubject extends Subject {
  ...

  public void hasFoo(Foo expected) {
    assertThat(actual.foo()).isEqualTo(expected);
  }
}

After:

class MyProtoSubject extends Subject {
  ...

  public void hasFoo(Foo expected) {
    check("foo()").that(actual.foo()).isEqualTo(expected);
  }
}

Benefits of check include:

• When the assertion fails, the failure message includes more context: The message specifies that the assertion was performed on myProto.foo(), and it includes the full value of myProto for reference.
• If the user of the assertion called assertWithMessage, that message, which is lost in the assertThat version, is shown by the check version.
• check makes it possible to test the assertion with ExpectFailure and to use Expect or assume. assertThat, by contrast, overrides any user-specified failure behavior.