GeezerVison

While working on this change, I encountered a design concern regarding the following logic:

public ThrowableAssertAlternative<T> isThrownBy(final ThrowingCallable throwingCallable) {
  Throwable throwable = Throwables.catchThrowable(throwingCallable);
  checkThrowableType(throwable);
  @SuppressWarnings("unchecked")
  T castThrowable = (T) throwable;
  return buildThrowableTypeAssert(castThrowable).as(description);
}

protected void checkThrowableType(Throwable throwable) {
  assertThat(throwable).as(description).hasBeenThrown().isInstanceOf(expectedThrowableType);
}

Originally, hasBeenThrown() is used to check whether an exception was thrown, and it’s implemented in AbstractThrowableAssert.

However, hasBeenThrown() only checks whether actual is null, which means it cannot include the expected exception type in the failure message — because actual itself is the thrown exception instance that would need to be checked.

protected SELF hasBeenThrown() {
  if (actual == null) {
    throw Failures.instance().failure(info, new BasicErrorMessageFactory("%nExpecting code to raise a throwable."));
  }
  return myself;
}

So I make a new method hasThrownExceptionOf(Class<? extends Throwable>), which accepts the expected exception type and produces a more informative failure message when no exception is thrown, such as:

Expecting code to throw java.lang.IllegalArgumentException, but no exception was thrown.

I’m open to suggestions if there’s a better way to include the expected exception type in the failure message.

Integrated thanks @simhani1 !