public void can_change_primary_specialty() { var subject = new Provider() { Id = 1 }; var specialtyA = new Specialty() { Id = 1 }; var providerSpecialtyA = subject.AddSpecialty(specialtyA); var specialtyB = new Specialty() { Id = 2 }; var providerSpecialtyB = subject.AddSpecialty(specialtyB); subject.SetPrimarySpecialty(providerSpecialtyB); Assert.IsFalse(providerSpecialtyA.IsPrimary); Assert.IsTrue(providerSpecialtyB.IsPrimary); }