[W09] Add tests for W09

[nilsreichardt]

Checklist

General

• I confirm that my tests, if any, are correct
  • Optional: I pass all artemis tests.
  • Optional: I pass all tests, that are added in this PR.
  • Optional: I calculated manually the correct solutions on paper.
• I chose a title conforming to the naming conventions for pull requests.
• The newly added tests do not reveal the solutions dynamically calculating the solutions as expected in the exercise.
• Other students approved this Pull Request.

Description

• Used the tests from last as foundation
• Refactored tests from last year
• Added a bunch of tests to ValidAVLTest.java
  • Added testValidAVLCorrect01
  • Added testValidAVLCorrect04
  • Added testValidAVLLoop01
  • Added testValidAVLLoop02
  • Added testValidAVLBalanceEqualsHeight01
  • Added testValidAVLBalanceEqualsHeight02
  • Added testValidAVLBalanceEqualsHeight03
  • Added testValidAVLBalanceEqualsHeight04
  • Added testValidAVLBalanceEqualsHeightOnlyRoot
• Added a few tests to InsertTest
  • Added testInsertLeftRight3
  • Added testInsertDuplicateKeys
• Added tests for the find method
• Added fix seed for Random object