The test classes use mix of Junit asserts and AssertJ. Since AssertJ assertions are more robust and extensive as compared to Junit5.

Like for example, usage of assertThatExceptionOfType from AssertJ is much more readable as compare to assertThrows from JUnit 5.

assertThatExceptionOfType(RuntimeException.class)
         .isThrownBy(() -> { throw new RuntimeException(new IllegalArgumentException("boom!")); })
         .havingCause()
         .withMessage("boom!");

We can migrate all the asserts from Junit to AsserJ.

Working on this issue

This issue affects several exercises. If you want to contribute to this issue, you don't have to change this in all exercises, feel free to submit small PRs fixing this issue for a single exercise or a small subset of exercises!