C# Unit Test Design Issue: How to reduce redundancy in unit test writing?

Question

Here is my c# unit test design issue:

I have one test that I want to run on some code that modifies a file. My test will run the code that modifies the file, then check the result. Pretty straight forward so far...

The issue is, I have about 10 files (soon to be a lot more) that I want to run the same unit test against. I dont want to write a new unit test for each file, when the test itself is really the same.

I could write a single test that queries the files in the folder and then runs the test logic on each file, but using this method would only report one pass/fail result for the entire set of files.

Id like to create some sort of dynamic system where every file that I place in a particular folder gets ran though this same unit test. So if 25 files are in the folder, the test gets ran 25 times, and the unit test reults report that 25 tests were ran, and includes seperate pass/fails for each.

Any ideas how or if this can be done in a c# unit test? Or with a nunit test?

Thanks! And I hope this is not a duplicate question. I looked around, but I could not find anything.

Answer 1

It sounds like what you need is a parameterised test case: see http://www.nunit.org/index.php?p=testCaseSource&r=2.5.

So:

[TestFixture]
public class Tests
{
    static string[] FileNames = new string[] 
                    { "mary.txt", "mungo.txt", "midge.txt" };

    [Test, TestCaseSource("FileNames")]
    public void TestMethod(string fileName)
    {
        Assert.That(File.Exists(fileName));
    }
}

The [TestCaseSource] attribute tells NUnit to get the values of the string parameter from the string array.

That approach, however, requires static constants for filenames. If you'd rather have a programmatic approach that reads the files from a database or suchlike try a factory class like so:

[TestFixture]
public class Tests
{
    [Test, TestCaseSource(typeof(FilenameFactory), "FileNames")]
    public bool FileCheck(string fileName)
    {
        return File.Exists(fileName);
    }
}

public class FilenameFactory
{
    public static IEnumerable FileNames
    {
        get
        {
            foreach (var filename in 
                   Directory.EnumerateFiles(Environment.CurrentDirectory))
            {
                yield return new TestCaseData(filename).Returns(true);
            }
        }
    }
}

The TestCaseData class generates "test cases" which have expectations that can be set through a fluent interface.