public bool Valid(string userName, string passWord)
 
 {
 
 if (string.IsNullOrEmpty(userName)) throw new ArgumentNullException("userName is null");
 
 var isValid = userName == "admin" && passWord == "123456";
 
 Log.Write(userName);
 
 return isValid;
 
 }

 
［Test]
 
 [ExpectedException(typeof(ArgumentNullException))]
 public void Vaild_Throw_Test()
 {
 MyLogin l = new MyLogin();
 l.Valid("", "123456");
 }

[Test]
public void Valid_Return()
{
 MockRepository mock = new MockRepository();
 var log = mock.DynamicMock<ILog>();
 using (mock.Record())
 {
 log.WriteLog("admin");
 LastCall.Return(0);
 }
 var returnValue = log.WriteLog("admin");
 Assert.AreEqual(returnValue, 0);
}