Get started with unit testing

Step 1. Add unit test project

In our example, we have a solution with a single project called Sandbox, which has a class that implements a primitive calculator:

namespace Sandbox
{
   public class Calculator
   {
       public static int Add(int x, int y) => x + y;
       public static int Subtract(int x, int y) => x - y;
   }
}

To test our calculator, let's start by creating a project for our unit tests.

Step 2. Write your first tests

In the test project, JetBrains Rider automatically created a file named UnitTest1.cs with a stub for our first test and opened it for you. We are ready to test our calculator.

Unit testing frameworks include a lot of functions to check how the target code works. The most straightforward way is to compare function's actual output against the expected value. NUnit provides Assert.AreEqual method for that.

Let's create two tests, PassingTest() that will compare the result of Add(2,2) against 4 and FailingTest() that will compare the result of Add(2,2) against 5:

using NUnit.Framework;
using Sandbox;

namespace Tests
{
    public class Tests
    {
        [Test]
        public void PassingTest()
        {
            Assert.AreEqual(4, Calculator.Add(2,2));
        }

        [Test]
        public void FailingTest()
        {
            Assert.AreEqual(5, Calculator.Add(2,2));
        }
    }
}

note

If you copy-paste this sample code to the unit test file, the Calculator usages will be highlighted as unresolved because the Sandbox project is not referenced in our test project. You can press Alt+Enter on the highlighted usage to add the missing project reference.

Step 3. Run the tests

Now that you've written the first tests, let's run them. You can click the unit test icon next to the test class and choose Run All to run all tests in that class.

JetBrains Rider will start the tests and bring up the Unit Tests window where you can see test progress and results.

Step 4. Analyze test results

As expected, the PassingTest has passed and the FailingTest has failed. Normally, you want to focus on failed tests.

Step 5. Next steps

As you write more tests, you may end up having lots of files in your test project, or you can even have multiple test projects in your solution. In such situation, using editor controls (as demonstrated above) will not be the most convenient way to run multiple tests. Instead, you can locate a solution, project, or any node containing unit tests in the Solution Explorer, right-click it and choose Run Unit Tests Ctrl+U, R. Or alternatively, you can browse all tests in the solution on the Explorer tab of the Unit Tests window and run tests from there: