Added recipe to use explicit isEmpty in AssertJ assertions

[pibizza]

What's changed?

I have added a new recipe to simplify assertions in tests that use AssertJ isEmpty().
Specifically, this recipe simplifies assertThat(collection.isEmpty()).isTrue() into assertThat(collection).isEmpty() and assertThat(collection.isEmpty()).isFalse() into assertThat(collection).isNotEmpty()

What's your motivation?

I work a lot with AssertJ and I have lots of legacy code to cleanup assertions.

Anything in particular you'd like reviewers to focus on?

This is similar to other recipes I have contributed, so there should be no big issue.

Anyone you would like to review specifically?

Have you considered any alternatives or workarounds?

Any additional context

Checklist

• I've added unit tests to cover both positive and negative cases
• I've added the license header to any new files through ./gradlew licenseFormat
• I've used the IntelliJ auto-formatter on affected files
• I've updated the documentation (if applicable)

[knutwannheden]

Apart from a few minor details this looks good to me.

We could consider creating a follow-up commit where we also apply this to CharSequence#isEmpty() and Optional#isEmpty() for which AssertJ AFAIK also has dedicated methods.

[pibizza]

All comments applied. I agree with @knutwannheden that we should add recipes for other cases - for example Optional needs recipes for isPresent() and isEmpty(). There is lots to do for assertj cleanup.

[murdos]

Apart from a few minor details this looks good to me.

We could consider creating a follow-up commit where we also apply this to CharSequence#isEmpty() and Optional#isEmpty() for which AssertJ AFAIK also has dedicated methods.

In fact we can even go further and migrate 'assertThat(string.size()).isEqualTo(0)' to 'assertThat(string).isEmpty()'

But I wonder if it belongs to the same recipe

[pibizza]

@murdos I think we can put this in the recipe to cleanup the size. I can take care of that.