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);
}