I am trying to create a function similar to Excel's [`EOMONTH`](http://office.microsoft.com/en-us/excel-help/eomonth-HP005209076.aspx) function in C#. I have written the following, however, I am not entirely sure if the it achieves the equivalent functionality. Is my equivalent of Excel's "Eomonth" function correct and are my tests sufficient?

```
public static DateTime EOMonth(this DateTime dateTime, int months = 0)
{
    DateTime firstDayOfTheMonth = new DateTime(dateTime.Year, dateTime.Month, 1);
    return firstDayOfTheMonth.AddMonths(1 + months).AddDays(-1);
}

```

**Tests**

```
[Test]
public void EOMonth_For5jan2011WithNoAddedMonths_ReturnsLastDayOfJan() 
{
    var expectedDate = DateTime.Parse("31-Jan-2011");
    var currentDate = DateTime.Parse("5-Jan-2011");

    var result = currentDate.EOMonth();

    Assert.That(result, Is.EqualTo(expectedDate));
}

[Test]
public void EOMonth_For5jan2011With_1_AddedMonths_ReturnsLastDayOfFeb2011()
{
    var expectedDate = DateTime.Parse("28-Feb-2011");
    var currentDate = DateTime.Parse("5-Jan-2011");

    var result = currentDate.EOMonth(1);

    Assert.That(result, Is.EqualTo(expectedDate));
}

[Test]
public void EOMonth_For5jan2011WithNegative_1_AddedMonths_ReturnsLastDayOfFeb()
{
    var expectedDate = DateTime.Parse("31-Dec-2010");
    var currentDate = DateTime.Parse("5-Jan-2011");

    var result = currentDate.EOMonth(-1);

    Assert.That(result, Is.EqualTo(expectedDate));
}

 [Test]
 public void EOMonth_For28Feb2007_12_AddedMonths_ReturnsLastDayOfFeb2008()
 {
     var expectedDate = DateTime.Parse("29-Feb-2008");
     var currentDate = DateTime.Parse("28-Feb-2007");

     var result = currentDate.EOMonth(12);

     Assert.That(result, Is.EqualTo(expectedDate));
 }

```