Visual Studio and Data Driven Unit Tests

Unit testing can be tedious when you have a battery of data to test against.  If you’re just testing against a small number of different data, then using Data Driven Unit Tests might be a bit overkill.  However, Data Driven Unit Tests gives you is a single location of data that can be used throughout your unit testing project.  Instead of modifying the data you typed in your unit test code, you can just modify it in your data file.  I used this MSDN entry as a starting point.

The method we’ll be testing is shown below.

Public Function SomeMethod(ByVal data As String) As Integer
   Return data.Length
End Function

You create the unit test for SomeMethod as usual.  Now what about our data file?  I’ll use an XML data file that just holds a few strings named test.xml.

<Samples>
    <Sample0>My Sample</Sample0>
    <Sample1>This is another sample</Sample1>
</Samples>

Now you have your simple data file.  To hook it into your unit test project, open up the Test List Editor in Visual Studio.  Find the test that you want to use test.xml with and click on that test.

In the Properties, find the Data Connection String entry and press the ellipses button.  This will bring up the New Test Data Source Wizard.

Select XML File and press Next to bring up the next screen.  Press the ellipses button and find test.xml.  This should fill in Table and Preview data for you.

Pressing Next will bring you to the final page of the wizard.  Highlight the table and press Finish.

You’ll see a dialog after the previous step.  Press Yes and Visual Studio will add test.xml to your unit test project.

If you look at your Data Connection String property, it should now point to test.xml within your unit test project.  The next step is using the data in your unit test.  Here’s a simple example of how to use your data.

<DataSource("Microsoft.VisualStudio.TestTools.DataSource.XML", "|DataDirectory|\test.xml", "Samples", DataAccessMethod.Sequential)> _
<DeploymentItem("TestProject1\test.xml")> _
<TestMethod()> _
Public Sub SomeMethodTest()
  Dim target As Form1 = New Form1
  Dim data As String = String.Empty

  Assert.IsTrue(target.SomeMethod(TestContext.DataRow("Sample0")) = TestContext.DataRow("Sample0").ToString.Length)
End Sub

The attributes for SomeMethodTest get automatically added when you add test.xml to your Data Connection String property.  The main point here is that TestContext.DataRow() is used to access your data.

One issue that I’ve run into was that I wanted to move my data into a sub folder called Data within my unit test project.  This will work, but the path to test.xml is a hard path.  Why does this matter?  I’m part of a team and having a hard path breaks the unit test since not all of our workspace paths are the same.  If you look at the Data Connection String property, you’ll notice that |DataDirectory| is at the beginning before the xml file location.  This transfers fine over different workspaces, however you’ll have to leave the data file where it gets inserted into the project by default.