Sure! I think knowing one unit testing framework and one mocking framework will meet 80% of what you'll need.
Most of the frameworks share similar ideas so if later you find that your team is using something different, it's very easy to transition to the next framework.
As a side note, the book Effective Java is a gold mine full of Java best practices. There are a lot of book summaries available online, but I ended up buying the book to support the author.
Good luck and wish you all the best!
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