Integration of automated tests into pipelines

In this guide, you’ll learn how to integrate MSTest-based automated tests into an Azure DevOps pipeline for a simple C# application. By enforcing tests in CI, every code change is verified and any failures block deployment before reaching production.

Converter Class Library

We start with a basic C# class library containing conversion methods:

namespace ConverterLib
{
    public class Converter
    {
        public double CelsiusToFahrenheit(double celsius)
        {
            return (celsius * (9.0 / 5.0)) + 32;
        }

        public double MetersToFeet(double meters)
        {
            return meters * 3.28004;
        }

        public double KilogramsToPounds(double kilograms)
        {
            return kilograms * 2.20462;
        }
    }
}

You can verify outputs locally with a small console runner.

Conversion Methods at a Glance

Setting Up the Azure DevOps Pipeline

In Azure DevOps, select Azure Repos Git as the source and point to the SimpleConverter repository:

Choose the .NET Desktop template to match our class library:

Here’s the initial azure-pipelines.yml for CI:

trigger:
- master

pool:
  vmImage: 'windows-latest'

variables:
  solution: '**/*.sln'
  buildPlatform: 'Any CPU'
  buildConfiguration: 'Release'

steps:
- task: NuGetToolInstaller@1

- task: NuGetCommand@2
  inputs:
    restoreSolution: '$(solution)'

- task: VSBuild@1
  inputs:
    solution: '$(solution)'
    platform: '$(buildPlatform)'
    configuration: '$(buildConfiguration)'

- task: VSTest@2
  inputs:
    platform: '$(buildPlatform)'
    configuration: '$(buildConfiguration)'

After committing, the pipeline runs successfully:

Pipeline Task Overview

Adding MSTest Unit Tests

Create a new MSTest project that references ConverterLib. Here’s a complete test class:

using ConverterLib;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace Converter.Tests
{
    [TestClass]
    public class ConverterTests
    {
        private Converter _converter;

        [TestInitialize]
        public void Setup()
        {
            _converter = new Converter();
        }

        [TestMethod]
        public void TestCelsiusToFahrenheit()
        {
            Assert.AreEqual(32, _converter.CelsiusToFahrenheit(0), 0.001, "0°C should be 32°F");
            Assert.AreEqual(212, _converter.CelsiusToFahrenheit(100), 0.001, "100°C should be 212°F");
        }

        [TestMethod]
        public void TestMetersToFeet()
        {
            Assert.AreEqual(3.28084, _converter.MetersToFeet(1), 0.00001, "1 meter ≈ 3.28084 feet");
        }

        [TestMethod]
        public void TestKilogramsToPounds()
        {
            Assert.AreEqual(22.0462, _converter.KilogramsToPounds(10), 0.001, "10 kg ≈ 22.0462 lb");
        }
    }
}

Run the tests locally to confirm they pass, then commit and push. The pipeline’s VSTest task will verify them in CI.

Demonstrating a Pipeline Failure

Introduce a faulty implementation for demonstration:

public double CelsiusToFahrenheit(double celsius)
{
    // Faulty return for demonstration
    return 4;
    // return (celsius * (9.0 / 5.0)) + 32;
}

A local build succeeds, but the console runner shows incorrect output:

Hello, World!
The temperature is 30 degrees, or 4 degrees Fahrenheit

When pushed, the VSTest step fails in Azure DevOps:

This enforcement blocks deployment until the logic error is fixed.

Avoiding Accidental Omissions

A pipeline without tests might look like:

trigger:
- master

pool:
  vmImage: 'windows-latest'

variables:
  solution: '**/*.sln'
  buildPlatform: 'Any CPU'
  buildConfiguration: 'Release'

steps:
- task: NuGetToolInstaller@1
- task: NuGetCommand@2
  inputs:
    restoreSolution: '$(solution)'
- task: VSBuild@1
  inputs:
    solution: '$(solution)'
    platform: '$(buildPlatform)'
    configuration: '$(buildConfiguration)'

# VSTest task removed -> logic errors go unchecked

Always include the VSTest@2 task to enforce your unit tests:

- task: VSTest@2
  inputs:
    platform: '$(buildPlatform)'
    configuration: '$(buildConfiguration)'

Conclusion

By integrating MSTest unit tests into your Azure DevOps YAML pipeline, you establish a robust CI process that catches logic errors early. This simple setup increases confidence in code quality and ensures that only tested code is deployed.

References

• Azure DevOps Pipelines YAML schema
• MSTest Unit Testing Framework
• Azure Repos Git
• Continuous Integration (CI) in Azure DevOps