Robust Link Checking: Implement A Test Server In Textlint

Aug 16, 2025 by Benjamin Cohen 58 views

Implement a Test Server for Reliable Link Checking in textlint

Hey guys! So, you know how we had some tests disabled in #156? Yeah, it wasn't ideal. The main culprit was https://httpstat.us/ being down, which threw a wrench in our link checking. To prevent this kind of disruption in the future, I propose we set up our own test server right here in the repository. Think of it as our little link-testing lab!

Why a Local Test Server?

Reliability is Key: Let's dive into why having a local test server is crucial for maintaining the robustness of our textlint rules, especially the no-dead-link rule. Relying on external services like httpstat.us introduces a significant point of failure. These services can go down unexpectedly, experience performance issues, or even change their behavior, leading to flaky and unreliable tests. When our tests fail due to an external service outage, it doesn't necessarily mean there's a bug in our code; it just means the external dependency isn't behaving as expected. This can be frustrating and time-consuming to debug, as we have to first determine whether the issue lies in our code or with the external service. By setting up a local test server, we eliminate this external dependency and gain full control over the testing environment. We can simulate various scenarios, such as successful responses (200 OK), client errors (400 Bad Request), server errors (500 Internal Server Error), and even network timeouts, all within a controlled and predictable environment. This allows us to thoroughly test our link checking logic and ensure it behaves correctly under different circumstances. Furthermore, a local test server enables us to run tests offline, which is particularly useful for developers working in environments with limited or no internet connectivity. This ensures that development and testing can continue without interruption. By investing in a local test server, we're investing in the long-term stability and reliability of our textlint rules. It provides a solid foundation for continuous integration and continuous delivery (CI/CD) pipelines, ensuring that our link checking functionality remains robust and accurate.

Full Control: Having our own server means we dictate the responses. We can simulate various HTTP status codes (200, 404, 500, you name it!) and ensure our textlint rule handles them gracefully.

Faster Testing: No more waiting on external services! Local tests are generally much quicker, speeding up our development workflow.

How to Implement It

The good news is that textlint-tester plays nicely with Mocha, so setting up the tests should be pretty straightforward. Here's a basic idea of how it could look:

// http//localhost4323
describe("no-dead-link", () => {
  let closeServer;
  before(async () => {
    closeServer = await startServer(); // "/200", "/500" etc...
  });
  after(() => {
    closeServer();
  })
  textlintTester.run(...
})

Let's break this down a bit more:

Setting up the Test Environment

The initial setup of the test environment is paramount for ensuring the reliability and consistency of our tests. In this phase, we define the lifecycle hooks that will manage the test server's state. The before hook, as the name suggests, runs before any of the tests within the describe block are executed. This is the perfect place to start our test server. We define an asynchronous function within the before hook that calls an startServer() function (which we'll implement later) and assigns the returned value to the closeServer variable. This startServer() function will be responsible for launching our Node.js test server and setting up the necessary routes to simulate different HTTP responses. The closeServer variable will hold a reference to a function that allows us to gracefully shut down the server when it's no longer needed. The after hook, on the other hand, runs after all the tests within the describe block have completed. This is where we want to clean up our test environment and ensure that no resources are left lingering. In our case, we use the after hook to call the closeServer() function, which will stop the Node.js test server and release any occupied ports or resources. By using the before and after hooks, we ensure that the test server is started before the tests run and stopped afterwards, providing a clean and isolated environment for each test suite. This helps to prevent test interference and ensures that our tests are reproducible and reliable. The describe block itself serves as a container for our tests related to the no-dead-link rule. It provides a logical grouping for our tests and allows us to organize them effectively. Within the describe block, we'll use the textlintTester.run() function to execute our test cases and assert the expected behavior of the no-dead-link rule. This setup ensures that our tests are well-structured and maintainable, making it easier to add new tests and debug existing ones.

Starting the Server (`startServer()`)

This function will be the heart of our test setup. It'll likely use Node.js and a lightweight framework like Express to create a simple web server. This server will have endpoints that return different HTTP status codes (e.g., /200 for a success, /404 for not found, /500 for a server error). This function is critical for simulating various scenarios that our no-dead-link rule might encounter. Imagine the power of being able to mimic server errors, redirects, and successful responses all within our test environment! To get this startServer() function up and running, we'll leverage the power of Node.js and a handy framework like Express. Think of Express as our trusty sidekick for building web applications quickly and easily. Inside startServer(), we'll spin up an Express app and define routes that correspond to different HTTP status codes. For example, we'll have a route for /200 that sends back a successful response, a route for /404 that simulates a "Not Found" error, and a route for /500 that mimics a server-side issue. This is where we get to be the puppet masters of our testing world, controlling exactly how the server responds to different requests. But it's not just about status codes. We can also customize the response bodies to include different types of content, simulate slow network connections, or even introduce intermittent errors. The possibilities are endless! The goal here is to create a robust and flexible testing environment that can handle any situation our no-dead-link rule might face in the wild. By carefully crafting our startServer() function, we can ensure that our tests are thorough, reliable, and give us the confidence that our link checking logic is rock solid. This will not only make our tests more effective, but also make our development process smoother and more enjoyable. So let's roll up our sleeves and build a startServer() function that will take our testing to the next level!

Closing the Server (`closeServer()`)

This function is crucial for cleaning up after our tests. It will shut down the Node.js server, freeing up the port and preventing conflicts with other tests or applications. Think of it as the responsible adult in the room, making sure everything is tidy before we leave. The closeServer() function plays a vital role in maintaining the integrity of our testing environment. Without it, we risk leaving our test server running in the background, potentially interfering with subsequent tests or even other applications that might be trying to use the same port. This can lead to flaky tests and make it difficult to reproduce issues consistently. When we shut down the server, we ensure that our testing environment is clean and isolated, allowing us to run tests with confidence. The implementation of closeServer() will depend on how we started the server in the first place. If we used Express, for example, the server object typically has a close() method that we can call to gracefully shut down the server. This method will stop the server from accepting new connections and allow any existing connections to complete before closing. By gracefully shutting down the server, we avoid abrupt disconnections that could lead to errors or data corruption. In addition to stopping the server, closeServer() might also be responsible for cleaning up any other resources that were created during the test setup, such as temporary files or databases. This ensures that our tests don't leave any unwanted traces behind and that our system remains in a consistent state. Think of closeServer() as the final step in our testing process, the moment when we put everything back in its place and prepare for the next round of tests. It's a small but essential function that contributes significantly to the overall reliability and maintainability of our testing infrastructure. So let's make sure we give closeServer() the attention it deserves and implement it carefully to ensure a clean and tidy testing environment.

Running the Tests (`textlintTester.run(...)`)

This is where the magic happens! We'll use textlintTester.run() to define our test cases. We can specify the rule to test (no-dead-link), the input text, and the expected errors. This is where we put our rule through its paces, throwing all sorts of link scenarios at it to see how it behaves. The textlintTester.run() function is the workhorse of our testing process, providing a structured and convenient way to define and execute test cases for our textlint rules. It allows us to specify the rule we want to test, the input text that the rule should process, and the expected errors or warnings that the rule should generate. This makes it easy to write comprehensive tests that cover a wide range of scenarios. When we call textlintTester.run(), we essentially provide it with a set of instructions on how to test our rule. These instructions include the name of the rule, the test cases (each consisting of input text and expected results), and any configuration options that should be applied to the rule during testing. The textlintTester then takes these instructions and executes the tests, comparing the actual output of the rule against the expected output. If the actual output matches the expected output, the test passes. Otherwise, the test fails, and we get a detailed error message that helps us identify the issue. The beauty of textlintTester.run() is that it handles all the complexities of running the tests, such as setting up the test environment, executing the rule, and comparing the results. This allows us to focus on writing meaningful test cases that thoroughly exercise our rule's functionality. We can create test cases that cover various scenarios, such as valid links, dead links, redirects, and different types of link formats. By carefully crafting our test cases, we can ensure that our rule behaves as expected in all situations and that we catch any potential bugs or edge cases. Think of textlintTester.run() as our personal testing assistant, taking care of the nitty-gritty details so we can concentrate on writing high-quality rules that improve the quality of our text. So let's embrace the power of textlintTester.run() and use it to create a robust and reliable testing suite for our no-dead-link rule.

Benefits of This Approach

More Reliable Tests: No more flaky tests due to external service outages.
Faster Feedback: Local tests run much quicker, giving us faster feedback on our changes.
Better Control: We have complete control over the testing environment, allowing us to simulate various scenarios.

Next Steps

I'm thinking we can start by:

Setting up a basic Node.js server with Express.
Creating endpoints for common HTTP status codes (200, 404, 500).
Integrating this server into our textlint-tester setup.

What do you guys think? Any suggestions or ideas are welcome! Let's make our link checking super robust!