Migrating Tests From JUnit 3 (GitAPITesCase) to JUnit 4 (GitAPITest)

[GAyan17]

JENKINS-60940 - Migrating Tests From JUnit 3 (GitAPITesCase) to JUnit 4 (GitAPITest)

Tests Migrated in this PR:

• RevList Tag
• RevList Local Branch
• Checkout Branch Null

Checklist

• I have read the CONTRIBUTING doc
• I have referenced the Jira issue related to my changes in one or more commit messages
• I have added tests that verify my changes
• Unit tests pass locally with my changes
• I have added documentation as necessary
• No Javadoc warnings were introduced with my changes
• No spotbugs warnings were introduced with my changes

Types of changes

• Tests (non-breaking change which updates dependencies or improves infrastructure)