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TDD 101
4. Testing the unpredictable
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Testing the unpredictable
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Testing the
unpredictable
Elements beyond our system:
• Randomness
• Time
• File system
You can’t rely on their behavior
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How can we test?
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1. Things that
are using
unpredictable
components
They are global state dependencies
Isolate and extract
Invert dependency
Stub for testing
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Example class User
{
private $id;
private $name;
public function __construct(string $name)
{
$this->id = Uuid::uuid4();
$this->name = $name;
}
}
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Example
class User
{
private $id;
private $name;
public function __construct(
UserId $id,
string $name
) {
$this->id = $id;
$this->name = $name;
}
}
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2. Things that
are
unpredictable
Don’t test what you don’t own
Test for properties of the output, not the
output itself
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Example class PasswordGeneratorTest extends TestCase
{
public function testShouldBeLongEnough()
{
$password = $this->generator->generate();
$this->assertTrue(strlen($password) > 9);
}
}
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Avoid coupling with
dependency inversion
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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.
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Thigh coupling
MyClass
Dependency
Uses
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Dependency inversion
MyClass
Interface
Dependency
Uses
Implements
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Dependency inversion & adapter pattern
MyClass
Interface Dependency
Uses
Implements
Adapter
Uses
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