In this article, let's learn about how to unit test
WebAPI in ASP.NET Core.
Table of Contents
- Why Unit Testing?
- What is a Middleware?
- When to use Middleware?
- Unit Testing Middleware
Unit testing is a crucial practice in software development that ensures the reliability and functionality of code components.
When it comes to
ASP.NET Core middleware, unit testing becomes essential for
that includes custom behavior. In this article, we will explore the importance of unit testing middleware, understand what middleware is, and provide practical examples
using C# to demonstrate how to effectively test ASP.NET Core middleware.
Why Unit Testing ?
Unit testing custom middleware allows developers to verify the behavior and functionality of their code. It provides confidence that the middleware functions as
intended, adding value to the application. Unit tests
catch bugs early in the development process,
for quick identification and resolution. By testing middleware, developers can
isolate and validate specific behaviors without
the need for complex integration testing, reducing the dependencies on external components.
Note: If you have not done so already, I recommend you read the article on Implementing TDD in C# .Net.
What is a Middleware ?
In the context of ASP.NET Core, middleware refers to components that are placed in the application's request pipeline. It sits between the client and the server,
processing requests and generating responses. Middleware performs various tasks, such as authentication, logging, exception
handling, and modifying HTTP headers. Each middleware component is responsible for a specific functionality, and they are executed sequentially as the request flows
through the pipeline.
Note: If you have not done so already, I recommend you read the article on Introducing Middleware in ASP.NET.
When to use Middleware ?
Custom middleware is often required when the
built-in ASP.NET Core middleware does not meet specific application requirements.
It allows developers to extend the request pipeline with their own logic. Some scenarios where custom middleware might be used include:
- Adding security headers to HTTP responses.
- Implementing custom logging or error handling.
- Modifying request or response data.
- Enforcing specific authorization rules.
Unit Testing Middleware
Let's consider an example of unit testing an ASP.NET Core middleware named
AddingSecurityHeadersMiddleware. This middleware
adds security headers to the HTTP response.
Code Sample - WebAPI Middleware
To begin, we create a test class called
AddSecurityHeadersMiddlewareTests and write a test method named
InvokeAsync_SetsExpectedResponseHeaders. In this test, we want to ensure that the expected response headers are added by the
Now let's add test to this middleware. The steps are,
In the test method, we set up the dependencies required for the test. This includes creating an instance of the
DefaultHttpContext and mocking the
RequestDelegate, which represents the
next middleware in the pipeline. To
isolate the test, we use an action that returns a
completed task instead of invoking the actual next middleware.
Next, we instantiate the middleware by passing the mocked
RequestDelegate to its
Then, we call the
InvokeAsync method of the middleware, passing the created
assert the values of the response headers added by the middleware by accessing the
collection of the
HttpContext. We compare the obtained values with the expected values using assertions.
Code Sample - WebAPI Middleware Test
custom ASP.NET Core middleware ensures the reliability and correctness of
the code. By testing middleware components, developers can verify their
behavior and functionality in isolation, reducing the need for complex
integration tests. Through practical examples and the use of mocking techniques, developers can effectively test their middleware, enhancing
the overall quality of ASP.NET Core applications.