public void ReturnNull_IfIdNotMatched()
{
// Arrange
var classes = this.GetClasses();
var queryable = classes.AsQueryable();
var mockedDbSet = new Mock <IDbSet <StudentClass> >();
mockedDbSet.As <IQueryable <StudentClass> >().Setup(m => m.Provider).Returns(queryable.Provider);
mockedDbSet.As <IQueryable <StudentClass> >().Setup(m => m.Expression).Returns(queryable.Expression);
mockedDbSet.As <IQueryable <StudentClass> >().Setup(m => m.ElementType).Returns(queryable.ElementType);
mockedDbSet.As <IQueryable <StudentClass> >().Setup(m => m.GetEnumerator()).Returns(() => queryable.GetEnumerator());
var mockedDbContext = new Mock <IDatabaseContext>();
mockedDbContext.Setup(c => c.StudentClasses).Returns(mockedDbSet.Object);
var studentClassService = new StudentClassService(mockedDbContext.Object);
// Act
var id = Guid.NewGuid().ToString();
var cl = studentClassService.FindById(id);
// Assert
Assert.IsNull(cl);
}