public async Task GetCourseAsync_CreatesMailingAndReturnsIt()
{
//arrange
var model = new GetMailingModel()
{
Name = "probability theory"
};
//act
var mail1 = await _service.GetCourseAsync(1);
var mail2 = await _service.GetCourseAsync(model);
// assert
Assert.IsTrue(_mailingsDb.ContainsValue(mail1));
Assert.IsTrue(_mailingsDb.ContainsKey(mail1.MailingId));
Assert.IsTrue(_mailingsDb.ContainsValue(mail2));
Assert.IsTrue(_mailingsDb.ContainsKey(mail2.MailingId));
}