Extreme Programming

int.TryParse

I had a situation where I had to use int.TryParse.  A field in the form that I will show later uses this method to convert a string value to integer.  I want to ensure that the value is correct.

set
{
    int intValue = 0;
    //If not an integer value, throw an exception
    if (!int.TryParse(this.txtReoccurrenceUnit.Text, out intValue))
        throw new ArgumentException("The unit value is not of the right type", "value");
    this.txtReoccurrenceUnit.Text = intValue.ToString();
}

So I whipped up a test to remove the possibility of a bug.  I created the following test, which worked successfully.  I was glad to find out that on the test "11X", TryParse evalutated to false, instead of removing faulty characters. 

[Test()]
public void TestIntTryParse()
{
    string value = "12";
    int intValue = -1;

    Assert.IsTrue(int.TryParse(value, out intValue));

    value = "11X";
    intValue = -1;

    Assert.IsFalse(int.TryParse(value, out intValue));

    value = "XXXY";
    intValue = -1;

    Assert.IsFalse(int.TryParse(value, out intValue));
}

But what about "11X", would it return 11, or -1 for no value?  I thought I read that was the case, so I add three more asserts to the test, to go along with the existing asserts:

Assert.AreEqual(12, intValue);
Assert.AreEqual(11, intValue);
Assert.AreEqual(-1, intValue);

The second test failed; the value was zero instead of eleven, so my test was wrong.  I correct the second test, changing 11 to 0, and see if the third test works.   It does not; it seems no value is 0, not -1, and so I correct that also, to get a green bar.