Web Forms: Fix Test Server Port Conflicts

Have you ever run your end-to-end tests locally for the @getodk/web-forms package, only to find that subsequent runs fail because the server is still chugging away on localhost:5174? It's a common frustration, especially when you're iterating quickly and just want to re-run those tests to catch a bug or verify a fix. The error message, Error: http://localhost:5174 is already used, is a clear indicator that the previous test run didn't shut down its associated web server cleanly. This article dives deep into why this happens, how to effectively resolve it, and how to ensure your local testing environment is always ready for action.

Understanding the Issue: Why Services Don't Shut Down Cleanly

The core of the problem lies in how the end-to-end testing setup, likely utilizing tools like Playwright, manages its development server. When you run a command like yarn workspace @getodk/web-forms test:e2e, it typically does two main things: it starts a web server to serve your application (or the parts relevant to the tests) and then executes the Playwright tests against that running server. The expected behavior is that once the tests are complete, the server should gracefully shut down, freeing up the port it was using. However, in some scenarios, this cleanup process doesn't happen as expected. This can be due to various reasons, including unhandled errors during the test execution, unexpected exits of the test runner itself, or even issues with how the server process is managed.

When a server process isn't terminated properly, it continues to occupy the designated port (5174 in this case). The next time you attempt to run the test:e2e command, the system tries to start a new server, but it encounters the port conflict. Since the port is already in use, the new server cannot start, and the test runner reports an error, halting the process. This effectively prevents you from running your tests until the lingering process is manually terminated. The provided reproduction steps, running yarn workspace @getodk/web-forms test:e2e && yarn workspace @getodk/web-forms test:e2e, perfectly illustrate this by attempting to run the command twice in quick succession, guaranteeing the second invocation will find the port occupied.

For developers working on the @getodk/web-forms package, this can significantly disrupt the development workflow. Instead of a seamless loop of code, test, fix, repeat, developers are forced to stop and manually investigate or kill rogue processes. This adds unnecessary friction and time to the development cycle. The goal is to achieve an environment where running tests is as straightforward as possible, allowing developers to focus on building and improving the web forms functionality without being bogged down by environmental issues. The expected behavior, as stated, is that re-running a test command should yield the same successful result as the previous run, indicating a clean slate each time.

The reuseExistingServer: true Configuration Option

One of the most direct solutions to the