avoid the overhead of generic parameters, use reflections instead or keep it more abstract -> how many type safety is really needed?
Try to avoid that many class objects needed as parameters

remove reflection based accesslogic from model classes

i.e.
protected List provideValidTestDTOs(){
//add book to existing student
return new TestEntry(new BookDTO(this.stundenId),(postCreateMethod)this::assertStudentHasBook));
}

private void assertStudentHasBook(){
Assertions.assertFalse(this.testStudent.getBooks().isEmpty());
}