Adding Test Classes

After this lesson you can

• Add an MSTest test project to a solution, with a reference to the project it tests
• Write a test class with [TestClass] and [TestMethod], and run it

Key takeaways

• dotnet new mstest -n TvRemote.Tests makes a test project, and dotnet add TvRemote.Tests reference TvRemote lets its tests see the app's classes.
• [TestClass] marks a class that holds tests, and [TestMethod] marks a public void method that is one test.
• A method without [TestMethod], or one that isn't public, isn't run as a test.
• Test Explorer finds tests only after the solution builds, so build it when the list is empty.

Here's the Television class from Planning Unit Tests, in a console app named TvRemote:

namespace TvRemote;

public class Television
{
    public const int LowestChannel = 3;
    public const int HighestChannel = 15;

    public bool IsOn { get; private set; }
    public int CurrentChannel { get; private set; } = LowestChannel;

    public void TurnOn()
    {
        IsOn = true;
    }

    public void TurnOff()
    {
        IsOn = false;
    }

    // Goes up one channel, from the highest back to the lowest, and returns the new channel.
    // While the TV is off, nothing changes.
    public int ChannelUp()
    {
        if (IsOn)
        {
            CurrentChannel = CurrentChannel == HighestChannel ? LowestChannel : CurrentChannel + 1;
        }
        return CurrentChannel;
    }

    // Changes to the channel, if the TV is on and the channel exists. Returns whether it changed.
    public bool ChangeChannel(int channel)
    {
        if (!IsOn || channel < LowestChannel || channel > HighestChannel)
        {
            return false;
        }
        CurrentChannel = channel;
        return true;
    }
}

Add a test project

From the folder that holds TvRemote:

dotnet new mstest -n TvRemote.Tests
dotnet add TvRemote.Tests reference TvRemote
dotnet new sln -n TvRemote
dotnet sln add TvRemote TvRemote.Tests

In Visual Studio: right-click the solution in Solution Explorer, Add > New Project..., choose MSTest Test Project, and name it TvRemote.Tests. Then right-click the test project's Dependencies, Add Project Reference..., and check TvRemote.

The test project's .csproj lists the MSTest package, the reference, and one handy line: a global using, so every test file can use MSTest's names without its own using line:

<ItemGroup>
  <PackageReference Include="MSTest" Version="4.0.2" />
</ItemGroup>

<ItemGroup>
  <Using Include="Microsoft.VisualStudio.TestTools.UnitTesting" />
</ItemGroup>

<ItemGroup>
  <ProjectReference Include="..\TvRemote\TvRemote.csproj" />
</ItemGroup>

(The template also adds Test1.cs, an empty example: delete it.)

Add a test class

Add TelevisionTests.cs to the test project:

namespace TvRemote.Tests;

[TestClass]
public class TelevisionTests
{
    [TestMethod]
    public void ChannelUp_WhenOn_GoesUpOneChannel()
    {
        Television tv = new Television();
        tv.TurnOn();

        int newChannel = tv.ChannelUp();

        Assert.AreEqual(4, newChannel);
    }
}

Two attributes, in square brackets, tell the test runner what to run:

• [TestClass] marks a class that holds tests.
• [TestMethod] marks a method that is one test. It's public and returns void. (It takes no parameters, unless it gets them from [DataRow], which Writing Tests shows.)

Methods without [TestMethod] are ordinary helpers: the runner doesn't run them as tests.

Television needs no using: the test class's namespace, TvRemote.Tests, is inside TvRemote, so C# finds TvRemote.Television by itself.

Run it

Run Test > Run All Tests in Visual Studio, or in the terminal:

dotnet test

Passed!  - Failed:     0, Passed:     1, Skipped:     0, Total:     1, Duration: 31 ms - TvRemote.Tests.dll (net10.0)

Test Explorer lists every test with a green check or a red cross. Double-click one to jump to its code, or right-click it to run just that test.

Common problems

Check yourself

2 questions to try on the lesson page.

So what

One command makes a test project, one more connects it to your app, and two attributes turn a class into tests. From here on, every class you write can have tests beside it.

Key terms

• Test Project
• [TestClass] and [TestMethod]
• Attribute

Cheat sheets

• Adding Test Classes