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+---
+title: >
+  Why write custom assertions in your tests?
+pubDate: 2023-07-03
+permalink: >
+  archive/2023/07/03/why-write-custom-assertions-in-your-tests
+tags:
+  - automated-testing
+---
+
+I'm refactoring some code on a client project - creating a Repository class to centralise some logic before implementing the next feature.
+
+The repository class is responsible for finding and returning any nodes with a specified field value and some base conditions (it must be the correct node type, published, etc.).
+
+## Adding a custom assertion
+
+I'm using PHPUnit's native assertions to check it returns a Collection (I regularly include the `illuminate/collections` library from Laravel in other projects) and that each item is an instance of a `NodeInterface`, but there isn't an assertion to check each node is of the correct type.
+
+My initial implementation was to loop over each node and use `assertSame` on its bundle before refactoring to create an array of unique bundle names and comparing it to my expected names:
+
+```php
+self::assertSame(
+  expected: [$nodeType],
+  actual: $haystack
+    ->map(fn (NodeInterface $item): string => $item->bundle())
+    ->unique()
+    ->toArray(),
+);
+```
+
+## Why write a custom assertion?
+
+Whilst this works, it likely won't be clear in the future what it's testing.
+
+My initial thought was to add a comment describing it, but then I decided to wrap it in a custom assertion - `assertContainsOnlyNodesOfType` - a private static function within my test class that wraps the native assertions.
+
+This approach makes the test more readable now and in the future and more domain-focused by giving it a descriptive name.
+
+It can be easily reused within the same test case or elsewhere.
+
+Although I only perform one assertion in this case, I can combine multiple assertions and perform any other required steps.
+
+Finally, I can contain any implementation details within the custom assertion. Here, I'm matching the result against an array of expected values, not just a single node type which is what I want. This detail can be contained within the assertion, making it easier to read and reuse in the future.