I have been given the task to evaluate codeFirst and possible to use for all our future projects. The evaluation is based on using codeFirst with an existing database.
The issue from what I can see is that you are throwing away the mock object and newing up a new instance
_studentRepository = new StudentRepository(ctx);
Perhaps add a method on the interface to add the context object and reuse the same instance that was injected in the constructor.
using (var ctx = new SchoolContext("SchoolDB"))
{
_studentRepository.Context = ctx;
var students = _studentRepository.GetAll().ToList();
return students;
}
}