feat: add mockito dependency if needed

[SimonVerhoeven]

What's changed?

Added addDependency for Mockito

What's your motivation?

In case a rewrite from JMockito to Mockito happens, the build does not break.

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

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 IDEA auto-formatter on affected files

[kunli2]

thanks for the update!