public void GetAllUsersTest()
{
//given
Client client1 = new Client("John", "Bush", 1);
Client client2 = new Client("Andrew", "Bush", 2);
Client client3 = new Client("Peter", "Bush", 3);
//when
usersList.AddClients(client1, client2, client3);
//then
List <Client> allUsers = usersList.GetAllClients();
Assert.IsTrue(allUsers.Count == 3);
Assert.IsTrue(allUsers.Contains(client1));
Assert.IsTrue(allUsers.Contains(client2));
Assert.IsTrue(allUsers.Contains(client3));
}