public void CallContextCoursesOnce()
{
// Arrange
var data = this.GetData();
var mockedSet = new Mock <DbSet <Course> >();
mockedSet.As <IQueryable <Course> >().Setup(m => m.Provider).Returns(data.Provider);
mockedSet.As <IQueryable <Course> >().Setup(m => m.Expression).Returns(data.Expression);
mockedSet.As <IQueryable <Course> >().Setup(m => m.ElementType).Returns(data.ElementType);
mockedSet.As <IQueryable <Course> >().Setup(m => m.GetEnumerator()).Returns(data.GetEnumerator());
var contextMock = new Mock <ApplicationDbContext>();
contextMock.Setup(c => c.Courses).Returns(mockedSet.Object);
var service = new AssignmentService(contextMock.Object);
// Act
service.GetAllCourses();
// Assert
contextMock.Verify(s => s.Courses, Times.Once);
}