Exception in MS Unit Test?

Question

I created a unit test for a method of my project. That method raises an exception when a file is not found. I wrote a unit test for that, but I'm still not able to pass the test when the exception is raised.

Method is

public string[] GetBuildMachineNames(string path)
{
    string[] machineNames = null;

    XDocument doc = XDocument.Load(path);

    foreach (XElement child in doc.Root.Elements("buildMachines"))
    {
        int i = 0;
        XAttribute attribute = child.Attribute("machine");
        machineNames[i] = attribute.Value;
    }
    return machineNames;
}

Unit Test

[TestMethod]
[DeploymentItem("TestData\\BuildMachineNoNames.xml")]
[ExpectedException(typeof(FileNotFoundException),"Raise exception when file not found")]
public void VerifyBuildMachineNamesIfFileNotPresent()
{
    var configReaderNoFile = new ConfigReader();
    var names = configReaderNoFile.GetBuildMachineNames("BuildMachineNoNames.xml");
}

Should I handle the Exception in the method or am I missing something else??

EDIT:

The path I am passing is not the one to find the file, so this test should pass... i.e. what if file not exists in that path.

Answer 1

In your unit test it seems that you are deploying an xml file: TestData\BuildMachineNoNames.xml which you are passing to the GetBuildMachineNames. So the file exists and you cannot expect a FileNotFoundException to be thrown. So maybe like this:

[TestMethod]
[ExpectedException(typeof(FileNotFoundException), "Raise exception when file not found")]
public void VerifyBuildMachineNamesIfFileNotPresent()
{
    var configReaderNoFile = new ConfigReader();
    var names = configReaderNoFile.GetBuildMachineNames("unexistent.xml");
}

Answer 2

By putting [ExpectedException(typeof(FileNotFoundException),"Raise exception when file not found")] attribute you are expecting that the method will throw an FileNotFoundException, if the FileNotFoundException not thrown Test will fail. Otherwise Test will be success.

Answer 3

I never really understood the point of ExpectedException. You should be able to catch exception in code rather than in attributes. It is a better practice and also allows you to do stuff after it is raised (e.g. more validations)... Also it would let you stop the code in debugger and check things out rather than need to ask in forums. :)

I'd use Assert.Throws( TestDelegate code );.
See here an example.