Examine the JUnit 4 source code and identify 3 design patterns used

I am seeking a freelancer to examine the JUnit 4 source code and identify three design patterns used.

Skills and experience required:
- Intermediate familiarity with JUnit 4 source code
- Proficient in identifying design patterns
- Strong knowledge of software design principles

Project requirements:
- Identify three design patterns used in the JUnit 4 source code
- No specific design patterns are required, any design patterns will do
- Provide a detailed report with the identified patterns

URL: https://github.com/junit-team/junit4

1. Identify the class or interface that plays a specific role in the design pattern. (List them under the design pattern name)
2. Describe the collaboration between the roles as found in the source code.
3. Identify where another class can be easily added and describe why it is useful to do so.

You can use this as a starting point

Under - Extension
TestDecorator
TestSetup

Under - Framework
Junit4TestAdapter


Please note that the client prefers a freelancer who can deliver a detailed report as the preferred method of receiving the identified patterns.