Integration Testing APIs

Integration Testing APIs

Integration testing is a form of automated testing.

Contrary to unit tests, we don’t test a single code unit (such as classes) independent from other units, but we test the interaction of multiple units and how well they integrate.

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When to use integration tests

The opinions when to use integration testing and when to use unit testing differ a bit depending who you ask.

Most of the time it is stated, that you should use integration tests and unit tests together to have the best test coverage.

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Using Integration tests for APIs

When doing integration tests with APIs we typically want to test the complete data flow including a HTTP Request, all the logic that happens on the server and the response.

We therefore need a way of accessing the service while it is running from the integration test.

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How To

1. We assume that there is an existing WebApi or MinimalApi project in your C# Solution.
2. Create a new unit test project.
3. Install the NuGet Package Microsoft.AspNetCore.Mvc.Testing in the unit test project.

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How To (2)

4. Inside your unit test classes you can use an instance of a HttpClient to access the API.

private readonly HttpClient _client =
  new WebApplicationFactory<Program>().CreateClient();

• WebApplicationFactory is a type imported from the NuGet Package Microsoft.AspNetCore.Mvc.Testing.
• Program references the class Program in your WebApi or MinimalApi project. It therefore needs to be publicly available, so the unit test project can reference it.

public class Program
{
    public static void Main(string[] args)
    {
        var builder = WebApplication.CreateBuilder(args);
        var app = builder.Build();

        MyEndpoints.Map(app);

        app.Run();
    }
}

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How To (3)

5. A simple integration test might look like this:

[Test]
public async Task GetCharacters_IsSuccessful()
{
  var response = await _client.GetAsync("/sw-characters");
  Assert.DoesNotThrow(() =>
    response.EnsureSuccessStatusCode());
}