Please help me understand this JUnit exam question

When studying for my upcoming exam I stumbled upon this question about JUnit in an old exam and I don't really get the point of it.

Given were the following pictures and the questions:

Class one

Class two

1. Explain which problem exists when testing 'Class A'
2. Develop a solution for the problem
3. Write a JUnit test to show if 'Method s' displays the String correctly.

Is it an error in the actual code logic or more with the interface not being implemented correctly?

Appreciate any insight!