Writing unit tests is a good software engineering practice. In this article, we will learn how to create a C# .NET Core application while adhering to the Test Driven Development (TDD) approach. In the TDD approach, before implementing a functionality, you write a unit test for it. For example, if you want to write a function to add two numbers, first you’ll write a failed unit test and then implement the functionality to pass the test.
In this post, we’ll create a Calculator Application. To start, let’s follow the folder structure as outlined below:
· CalculatorApp – Solution
· CalculatorApp.Services – Application project
· CalculatorApp.Services.Tests – Test project
You can use Visual Studio to create projects; however, in this post, I will use .NET Core commands to create my projects, add tests, and run tests. You can also use MSTest or NUnit to write unit tests, but in this example, I’ll use xUnit and dotnet test to write and run my Unit Tests.
Let’s start by opening a command shell and follow along:
Creating the Application project
To start, you’ll need to create a directory called CalculatorApp. Keep in mind that you can follow any naming convention you’d like for directories, but if you’d like to follow along with this post, I would recommend following the same directory name. So, let’s create the CalculatorApp directory and navigate to it.
Inside the CalculatorApp directory, we are going to create a new solution by running the following command:
dotnet new sln
After successfully running the command, you should get the message “The Template Solution File was created successfully”. Also inside the CalculatorApp directory, you will find a file named calculatorapp.sln.
Next, create a directory called CalculatorApp.Services. This directory will keep the application sources i.e. all classes of the calculator application. Navigate to the Calculatorapp.Services directory and create a class library by running the following command:
dotnet new classlib
After successfully running this command, you should get the message “The Template Class Library was created successfully”. You’ll also find a file named calculatorapp.services.csproj inside the CalculatorApp.Services directory. Next, you need to add this class library project to the calculatorapp solution. To do this, navigate back to the calculatorapp directory, and run the command:
dotnet sln add .\calculatorapp.services\calculatorapp.services.csproj
After successfully running the command, you should get the message “Project added to the solution”.
Inside the CalculatorApp.Services folder, you will find a class Class1 – rename it to Calculator and modify the class as shown in the listing below:
You’ll notice in the above listing that the Add and Sub functions are not implemented. First, we will write a unit test and then implement these functionalities.
Creating the Test project
To add test projects, create a directory called CalculatorApp.Services.Tests and navigate to the directory. In this directory, we will create an MS Test project by running the following command:
dotnet new mstest
This command creates the test project which uses MS Test as the test library. Once the test project is created, add the source project library in the test project. To do that, run the command:
dotnet add reference ../CalculatorApp.Services/CalculatorApp.Services.csproj
This command will add a reference of the CalculatorAppService project into the test project. After adding the reference, add the test project to the solution by navigating to the calculatorapp root directory, and run the command:
dotnet sln add .\CalculatorAppServices.tests\CalculatorAppServices.Tests.csproj
This command will add the test project to the solution. After successfully running the command, you should get the message “Project added to the solution”.
Writing Unit Tests
So far, we’ve created the application source project and a test project. In the application source project, there are unimplemented functions. Now let us write tests for these functions.
In the Test project, I have renamed the file UnitTest1.cs to Ca