Integration tests for .NET CLI tools

Published on: January 22, 2023

I’ve spent Saturday evening working on a small project. I’ve built a .NET clone of tree utitly. You know, the one that renders a nice tree view for a given directory.

The project is available on GitHub under the dtree name. It’s a .NET global tool that you can install with the following command:

dotnet tool install -g dtree

The tool is pretty simple. It takes a path to a directory as an argument and renders a tree view for it. Here is an example:

dtree -a
📁 .
├── 📁 .devcontainer
│   └── devcontainer.json
├── 📁 .github
│   └── 📁 workflows
│      └── build-and-publish.yml
├── 📁 src
│   ├── dtree.csproj
│   ├── Program.cs
│   └── TreeNode.cs
├── .gitignore
├── LICENSE
└── README.md

The codebase is quite hacky. It’s a single file with top level statements. Not much abstractions over the System.Console and System.IO.Directory libraries. However, I wanted to make sure that it works as expected. So, I’ve added a few integration tests to the project.

I wanted to build tests that run the compiled tool and compare the output with the expected result. One would expect to have something similar to ASP.NET WebApplicationFactory. However, there is no such thing for .NET CLI tools. So, I had to come up with a solution.

I’ve created a new project, that won’t reference the dtree project directly. Instead, it will use the CliRunner wrapper around Process object that will execute dotnet run command to compile and run the dtree tool.


using System.Diagnostics;

namespace dtree.IntegrationTests;

public class CliRunner
{
    private readonly string cliProjectPath;
    private readonly Process process;

    public CliRunner(string cliProjectPath)
    {
        this.cliProjectPath = cliProjectPath;

        process = new Process();
        process.StartInfo.FileName = "dotnet";
        process.StartInfo.UseShellExecute = false;
        process.StartInfo.RedirectStandardOutput = true;
    }

    public (int exitCode, string output) Run(string args)
    {
        process.StartInfo.Arguments = $"run --project {cliProjectPath} -- {args}";

        process.Start();
        var output = process.StandardOutput.ReadToEnd();

        process.WaitForExit();

        return (process.ExitCode, output);
    }
}

And this wrapper can be used in tests.

using Xunit.Abstractions;

namespace dtree.IntegrationTests;

public class DTreeTests
{
    private readonly string cliProjectPath;
    private readonly CliRunner runner;

    public DTreeTests(ITestOutputHelper output)
    {
        cliProjectPath = Path.Combine(Directory.GetCurrentDirectory(), "../../../../src/dtree.csproj");
        output.WriteLine($"{cliProjectPath}");
        runner = new CliRunner(cliProjectPath);
    }

    [Theory]
    [InlineData("-d")]
    [InlineData("--max-depth")]
    public void Negative_Depth_Results_As_Error(string key)
    {
        var (exitCode, output) = runner.Run($"{key} -1");

        Assert.Equal($"😱 Max depth must be greater than 0{Environment.NewLine}", output);
        Assert.Equal(1, exitCode);
    }

    [Theory]
    [InlineData("-a")]
    [InlineData("--all")]
    public void All_Files_Should_Be_Included(string key)
    {
       var (exitCode, output) = runner.Run($"{key} -p ../../../../");

        Assert.Contains("📁 .devcontainer", output);
        Assert.Contains("📁 .github", output);
        Assert.Contains("📁 src", output);
        Assert.Contains(".gitignore", output);
        Assert.Contains("LICENSE", output);
        Assert.Contains("README.md", output);
        Assert.Equal(0, exitCode);
    }
}

This way I can run the tests in CI

    steps:
      - uses: actions/checkout@v3
        name: 📥 Checkout
      - name: 🧪 Execute Unit Tests
        run: dotnet test ./tests

And be sure to publish the package to NuGet if everything goes well.

Give it a try 🙂

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