91 lines
2.1 KiB
Markdown
91 lines
2.1 KiB
Markdown
---
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title: >
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Avoiding over-mocking
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pubDate: 2023-11-16
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permalink: >-
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archive/2023/11/16/avoiding-over-mocking
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tags:
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- software-development
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- automated-testing
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- test-driven-development
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---
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In unit tests, and sometimes in kernel tests, you need to mock the dependencies you aren't testing, but you can over-mock and only be testing the mocks and not the code you want to test.
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Here's an example (thanks, ChatGPT, for the code).
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## The Class to be tested (MyClass.php)
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```php
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<?php
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class MyClass {
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public function __construct(
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private DependencyInterface $dependency
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) {
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}
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public function doSomething() {
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$result = $this->dependency->performAction();
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return "Result: " . $result;
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}
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}
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```
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## Dependency Interface (DependencyInterface.php)
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```php
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<?php
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interface DependencyInterface {
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public function performAction();
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}
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```
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## A test class that ends up testing mocks (MyClassTest.php)
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```php
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<?php
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use PHPUnit\Framework\TestCase;
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class MyClassTest extends TestCase {
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public function testDoSomething() {
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// Creating a mock of the DependencyInterface.
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$dependencyMock = $this->createMock(DependencyInterface::class);
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// Setting up the mock to return a specific value.
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$dependencyMock->expects($this->once())
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->method('performAction')
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->willReturn('Mocked result');
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// Creating an instance of MyClass with the mock.
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$myClass = new MyClass($dependencyMock);
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// Calling the method to be tested.
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$result = $myClass->doSomething();
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// Asserting that the result matches the expected value.
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$this->assertEquals('Result: Mocked result', $result);
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}
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}
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```
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## Here's the thing
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In this example, the test creates a mock for the `DependencyInterface` and sets up an expectation that the performAction method will be called once, returning a specific value.
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The test then calls the `doSomething` method on `MyClass` and asserts that the result is as expected.
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The issue with this test is that it's not testing the actual behaviour of `MyClass`.
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It's only testing that the mock is configured correctly.
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If the real implementation of `MyClass` has a bug, this test won't catch it.
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