oliverdavies.uk/content/node.1fd87ecf-4269-4874-859e-d49c238694bf.yml

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title:
  - value: |
      Avoiding over-mocking
created:
  - value: '2023-11-16T00:00:00+00:00'
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  - value: '2025-05-11T09:00:28+00:00'
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body:
  - value: |
      <p>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.</p>

      <p>Here's an example (thanks, ChatGPT, for the code).</p>

      <h2 id="the-class-to-be-tested-myclass.php">The Class to be tested (MyClass.php)</h2>

      <pre><code class="language-php">&lt;?php

      class MyClass {

        public function __construct(
          private DependencyInterface $dependency
        ) {
        }

        public function doSomething() {
          $result = $this-&gt;dependency-&gt;performAction();

          return "Result: " . $result;
        }
      }
      </code></pre>

      <h2 id="dependency-interface-dependencyinterface.php">Dependency Interface (DependencyInterface.php)</h2>

      <pre><code class="language-php">&lt;?php

      interface DependencyInterface {

        public function performAction();

      }
      </code></pre>

      <h2 id="a-test-class-that-ends-up-testing-mocks-myclasstest.php">A test class that ends up testing mocks (MyClassTest.php)</h2>

      <pre><code class="language-php">&lt;?php

      use PHPUnit\Framework\TestCase;

      class MyClassTest extends TestCase {

        public function testDoSomething() {
          // Creating a mock of the DependencyInterface.
          $dependencyMock = $this-&gt;createMock(DependencyInterface::class);

          // Setting up the mock to return a specific value.
          $dependencyMock-&gt;expects($this-&gt;once())
            -&gt;method('performAction')
            -&gt;willReturn('Mocked result');

          // Creating an instance of MyClass with the mock.
          $myClass = new MyClass($dependencyMock);

          // Calling the method to be tested.
          $result = $myClass-&gt;doSomething();

          // Asserting that the result matches the expected value.
          $this-&gt;assertEquals('Result: Mocked result', $result);
        }

      }
      </code></pre>

      <h2 id="here%27s-the-thing">Here's the thing</h2>

      <p>In this example, the test creates a mock for the <code>DependencyInterface</code> and sets up an expectation that the performAction method will be called once, returning a specific value.</p>

      <p>The test then calls the <code>doSomething</code> method on <code>MyClass</code> and asserts that the result is as expected.</p>

      <p>The issue with this test is that it's not testing the actual behaviour of <code>MyClass</code>.</p>

      <p>It's only testing that the mock is configured correctly.</p>

      <p>If the real implementation of <code>MyClass</code> has a bug, this test won't catch it.</p>

              
    format: full_html
    processed: |
      <p>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.</p>

      <p>Here's an example (thanks, ChatGPT, for the code).</p>

      <h2 id="the-class-to-be-tested-myclass.php">The Class to be tested (MyClass.php)</h2>

      <pre><code class="language-php">&lt;?php

      class MyClass {

        public function __construct(
          private DependencyInterface $dependency
        ) {
        }

        public function doSomething() {
          $result = $this-&gt;dependency-&gt;performAction();

          return "Result: " . $result;
        }
      }
      </code></pre>

      <h2 id="dependency-interface-dependencyinterface.php">Dependency Interface (DependencyInterface.php)</h2>

      <pre><code class="language-php">&lt;?php

      interface DependencyInterface {

        public function performAction();

      }
      </code></pre>

      <h2 id="a-test-class-that-ends-up-testing-mocks-myclasstest.php">A test class that ends up testing mocks (MyClassTest.php)</h2>

      <pre><code class="language-php">&lt;?php

      use PHPUnit\Framework\TestCase;

      class MyClassTest extends TestCase {

        public function testDoSomething() {
          // Creating a mock of the DependencyInterface.
          $dependencyMock = $this-&gt;createMock(DependencyInterface::class);

          // Setting up the mock to return a specific value.
          $dependencyMock-&gt;expects($this-&gt;once())
            -&gt;method('performAction')
            -&gt;willReturn('Mocked result');

          // Creating an instance of MyClass with the mock.
          $myClass = new MyClass($dependencyMock);

          // Calling the method to be tested.
          $result = $myClass-&gt;doSomething();

          // Asserting that the result matches the expected value.
          $this-&gt;assertEquals('Result: Mocked result', $result);
        }

      }
      </code></pre>

      <h2 id="here%27s-the-thing">Here's the thing</h2>

      <p>In this example, the test creates a mock for the <code>DependencyInterface</code> and sets up an expectation that the performAction method will be called once, returning a specific value.</p>

      <p>The test then calls the <code>doSomething</code> method on <code>MyClass</code> and asserts that the result is as expected.</p>

      <p>The issue with this test is that it's not testing the actual behaviour of <code>MyClass</code>.</p>

      <p>It's only testing that the mock is configured correctly.</p>

      <p>If the real implementation of <code>MyClass</code> has a bug, this test won't catch it.</p>

              
    summary: null
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