Testing Warp Web Applications: A Journey from Mocks to Reality
When it comes to testing web applications, especially those with external dependencies, it’s essential to have a solid strategy in place. In this tutorial, we’ll explore various integration testing techniques for Warp web applications, focusing on end-to-end tests that evaluate the entire system.
The Importance of Testing
Testing is a crucial aspect of software development, ensuring that our applications work as expected. With Warp, we need to consider not only the application itself but also its interactions with external dependencies, such as databases and HTTP services. In this article, we’ll delve into the world of testing, demonstrating how to test a Warp web application from scratch.
Building a To-Do App
To illustrate these concepts, we’ll create a simple to-do app that features a database and an external HTTP service call. We’ll start by building a small application, and then move on to testing it using various techniques.
Mocking Dependencies
When dealing with external dependencies, one common approach is to mock them away. We can do this by using traits or one of the many mocking libraries available for Rust. Mocks are useful, but they’re not the real thing. If our mock implementation is buggy or incomplete, we may miss some edge cases.
Using Real Dependencies
On the other hand, using real databases and external web services for automated testing comes with its own set of problems, such as providing infrastructure, test reproducibility, and speed. However, this approach allows us to test our application in a more realistic environment.
A Hybrid Approach
To get the best of both worlds, we’ll take a hybrid approach, starting with simple mocks and gradually moving towards more sophisticated fakes and real dependencies. We’ll use the wiremock library to simulate external web services, allowing us to define expected responses while still executing real HTTP requests.
Testing with Mocks
We’ll start by creating a test module inside our application’s source code, adding it to our main.rs file. This means the module is only loaded for tests and won’t show up in our binary. We’ll implement two hardcoded versions of our database and HTTP abstractions, and then write simple tests for our two handlers using the warp::test utilities.
Testing with Wiremock
Next, we’ll use wiremock to send real HTTP requests to our application. We’ll create a thin wrapper around wiremock, allowing us to spawn a wiremock server on demand and access it from anywhere. We’ll register a mock for the /facts/given endpoint, which will return a predefined response.
Testing with a Real Database
To take our testing to the next level, we’ll use a real Postgres database. We’ll create a helper function to connect to the database, reset it, and return an instance to be used in our tests. We’ll then write tests that use a real database and send real HTTP requests.
Full End-to-End Testing
Finally, we’ll go full end-to-end, testing our running web service with all the real things. We’ll create a Server abstraction, which starts the crate’s run method on the first call, and an initrealserver helper, which clears the database and ensures the server is up. We’ll then send HTTP requests to our web service using hyper.
Conclusion
Testing is a complex topic, and there’s no one-size-fits-all approach. By using a mix of unit, integration, and end-to-end testing techniques, we can ensure our applications work as expected. In this tutorial, we’ve demonstrated various integration testing techniques for Warp web applications, ranging from simple mocks to fully integrated end-to-end tests.