How to get the handle for 'this' when testing a constructor

class MyClass
{
  //Constructor
  public MyClass(string paramB)
  {
    if (paramB.Length > PropertyX)  thorow new ArgumentException();

    .... Code ....
    .... Code ....
  }

  public int PropertyX
  {
    get
    {
      int retVal = 0;
      ...<Code>...
      return retVal;
    }
  }
  
}

// Objective of this test is to make sure that 'ArgumentException' is thorwn in case if passed parameter's length gets bigger than PropertyX's value
[TestMethod()]
public void MyClassTest_TextLenMoreThanLimit_ThrowArgumentException()
{
   string paramB = "20 char long string";

   MyClass myObj = null;

   try
   {
     myObj = new MyClass(paramB);
   }
   Catch(Exception e)
   {
       Assert.AreEqual(typeof(ArgumentException), e.GetType());
       return;
    }
   Assert.Fail("Failed to return ArgumentException");
}

[TestMethod(), VerifyMocks()]
public void MyClassTest_TextLenMoreThanLimit_ThrowArgumentException()
{
   string paramB = "20 chars. long string";

   MyClass myObj = null;

   using (RecordExpectations r = RecorderManager.StartRecording())
   {
     r.ExpectAndReturn(myObj.PropertyX, 19);
   }

   try
   {
     myObj = new MyClass(paramB);
   }
   Catch(Exception e)
   {
       Assert.AreEqual(typeof(ArgumentException), e.GetType());
       return;
    }
   Assert.Fail("Failed to return ArgumentException");
}