How to write your first C# Unit Test with Visual Studio?

Visual Studio makes Unit Testing easy by bundling a Unit Test framework into it.

Imagine you have a string extension method as shown below and you wanted to unit test it.

using System;

namespace ConsoleApplication1
{
    public static class StringExtensions
    {
        public static bool IsPrimaryColor(this string inString)
        {
            string[] primaryColors = { "Red", "Yellow", "Blue" };
            foreach (var color in primaryColors)
            {
                if (inString.Equals(color, StringComparison.CurrentCultureIgnoreCase))
                    return true;
            }
            return false;
        }
    }
}

Creating a Unit Test project to test this method is very easy.

Step 1 – Create a C# Unit Test Project

  1. In Visual Studio (assuming you already have a project open), click on the Solution and choose Add new project.
  2. Select Templates | Visual C# | Test from the menu on the left.
  3. Select Unit Test Project.
  4. Enter a name for the project.
    Note: Use a good name convention, such as naming the test project the same as the project it tests but with “Tests” at the end.  For example if you have a project called MyProject you would name your test project MyProjectTests. No, it isn’t rocket science. We like to keep it simple.
  5. Click OK.

Step 2 – Give your Unit Test project a reference to the project to test

  1. Right-click on References under the newly created Unit Test project and choose Add reference.
  2. Select Solution from the right.
  3. Add the project you plan to test as a reference.

Step 3 – Create your C# test class and first test method

  1. A test class was already created by default called UnitTest1.cs. Feel free to rename it to an appropriate name.
    Note: Use a good name convention, such as naming the test class the same as the class it tests but with “Tests” at the end.  For example if you have an object called MyObject you would name your test project MyObjectTests.
  2. Add a using statement to reference the namespace of the class you plan to test.
  3. Rename the first Test method. You can’t miss it. It has the [TestMethod] attribute.
    Note: Use a good name convention, such as naming the test method so clearly that you know what it is testing just by the name. For example, StringExtensionIsBlueAPrimaryColorTest().
  4. Add code to make your first test. It is recommended you create your method using the Arrange, Act, Assert pattern.
  5. Add additional test methods as needed.
    using ConsoleApplication1;
    using Microsoft.VisualStudio.TestTools.UnitTesting;
    
    namespace StringExtensionTests
    {
        [TestClass]
        public class UnitTest1
        {
            [TestMethod]
            public void StringExtensionIsBlueAPrimaryColorTest()
            {
                // Arrange
                string color = "Blue";
    
                // Act
                bool actual = color.IsPrimaryColor();
    
                // Assert
                const bool expected = true;
                Assert.AreEqual(expected, actual);
            }
    
            [TestMethod]
            public void StringExtensionIsRedAPrimaryColorTest()
            {
                // Arrange
                string color = "Red";
    
                // Act
                bool actual = color.IsPrimaryColor();
    
                // Assert
                const bool expected = true;
                Assert.AreEqual(expected, actual);
            }
    
            [TestMethod]
            public void StringExtensionIsYellowAPrimaryColorTest()
            {
                // Arrange
                string color = "Yellow";
    
                // Act
                bool actual = color.IsPrimaryColor();
    
                // Assert
                const bool expected = true;
                Assert.AreEqual(expected, actual);
            }
    
            [TestMethod]
            public void StringExtensionIsBlackAPrimaryColorTest()
            {
                // Arrange
                string color = "Black";
    
                // Act
                bool actual = color.IsPrimaryColor();
    
                // Assert
                const bool expected = false;
                Assert.AreEqual(expected, actual);
            }
        }
    }
    

You have now created your first Unit Test. Go ahead and run it. You should be able to run it in Visual Studio starting with VS 2012. If you have an earlier version, you can run tests using other tools.

Thorough Unit Testing

OK. Now let’s think about what tests would be valid that we don’t have? Here are a few:

  • Case insensitive. All the following strings should return true: Red, red, rEd.
  • What if the string is blank? Null? Junk characters?

Now you write additional unit tests to test this method.

Note: It is too bad that Visual Studio’s MSTest doesn’t support Row tests. NUnit does support Row tests. With Row tests, the above Unit Test code would involve a single method that passing in multiple string values.

2 Comments

  1. Vipasha says:

    I really liked this example it was less complicated than one which is in MSDN.

  2. Ogro says:

    You can simulate row tests by separating the test method out into a generalized version sans TestMethod attribute, and adding a row test version with the attribute that calls the generalized version with the appropriate parameters. It's more work than NUnit, but if you're using MSTest, then it's certainly better than nothing.

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