Verifying ArgumentException and its message in Nunit , C#

Question

In my test program in Nunit, I want to verify that it's getting the write Argument Exception by verifying the message.

    [Test]
    public void ArgumentsWorkbookNameException()
    {
        const string workbookName = "Tester.xls";
        var args = new[] { workbookName, "Sheet1", "Source3.csv", "Sheet2", "Source4.csv" };
        Assert.Throws(typeof(ArgumentException), delegate { var appargs = new ApplicationArguments(args); }, "Invalid ending parameter of the workbook. Please use .xlsx");

    }

After testing this out, this doesn't work when I modified the message in the main program.

        int wbLength = args[0].Length;

        // Telling the user to type in the correct workbook name file.
        if (args[0].Substring(wbLength-5,5)!=".xlsx")
        {
            throw new ArgumentException(
                "Invalid ending parameter of the workbook. Please use .xlsx random random");
        }

The unit test still passed, regardless if I changed the message.

How do I do it? Or is there no such things in C#. My colleague said there are options like that in Ruby and RSPEC, but he's not 100% sure on C#.

Answer 1

Use the fluent interface to create assertions:

Assert.That(() => new ApplicationArguments(args), 
    Throws.TypeOf<ArgumentException>()
        .With.Message.EqualTo("Invalid ending parameter of the workbook. Please use .xlsx random random"));