docs(daily-email): add 2022-12-30

website/src/daily-emails/2022-12-30.md

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+---
+title: >
+  Tests are living documentation
+pubDate: 2022-12-30
+permalink: >
+  archive/2022/12/30/tests-are-living-documentation
+tags:
+  - testing
+---
+
+Today I was working on a project and made a one-line change that updated a single value within an API response.
+
+Unexpectedly, it caused a test to fail. The API response returned a 500 status code instead of the expected 201 code.
+
+I reverted the change locally and ensured that the test passed again, so I knew it was causing the failure.
+
+## Fixing the failure
+
+The change was removing a hard-coded part of a URL to a dynamic one, using Drupal's `Settings` class.
+
+I was retrieving a value from it, but as there was no value being set within the test, it was returning a null value and causing the 500 error code.
+
+## How does the Settings class work?
+
+To fix the test failure, I needed to learn how to set a Settings value within a test.
+
+To do this, I looked for and found the test for the Settings class itself. I saw how it was being set there, did the same in my test, fixed the failure and got my test passing again.
+
+## Tests are living documentation
+
+As well as verifying things work when they are written, tests also act as long-term documentation. They can be run at any point to ensure that they still pass and are a reference to other developers on how the code should work.
+
+Rather than a Confluence page, a README file or code comments which can become out of date, if a test becomes outdated, it will fail and make developers aware, as well as break any CI pipeline that it runs in.
+
+By writing tests, you're ensuring that your code works as expected and documenting it at the same time.