Testing the unpredictable
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This document discusses testing unpredictable elements like randomness, time, and file systems by isolating dependencies and inverting them. It provides examples of generating a user ID, testing password length without relying on the specific output, and using dependency inversion through interfaces and adapters to avoid tight coupling when testing unpredictable components.
Testing the unpredictable
- 1. TDD 101 4. Testing the unpredictable
- 3. Testing the unpredictable Elements beyond our system: • Randomness • Time • File system You can’t rely on their behavior
- 4. How can we test?
- 5. 1. Things that are using unpredictable components They are global state dependencies Isolate and extract Invert dependency Stub for testing
- 6. Example class User { private $id; private $name; public function __construct(string $name) { $this->id = Uuid::uuid4(); $this->name = $name; } }
- 7. Example class User { private $id; private $name; public function __construct( UserId $id, string $name ) { $this->id = $id; $this->name = $name; } }
- 8. 2. Things that are unpredictable Don’t test what you don’t own Test for properties of the output, not the output itself
- 9. Example class PasswordGeneratorTest extends TestCase { public function testShouldBeLongEnough() { $password = $this->generator->generate(); $this->assertTrue(strlen($password) > 9); } }
- 10. Avoid coupling with dependency inversion
- 11. Dependency Inversion High level modules should not depend on low level modules, both should depend on abstractions. Abstractions should not depend on details. Details should depend on abstractions.
- 14. Dependency inversion & adapter pattern MyClass Interface Dependency Uses Implements Adapter Uses