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TDD 101
5. Low cost techniques for doubles
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Low cost techniques for
doubles
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The point of
going low-cost
Test should be
• Light
• Fast
• Easy to read
• Easy to maintain
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The point of
going low-cost
Reduce dependency on mocking
frameworks
Strictly speaking, mocking frameworks
break isolation principle
Use the things you have at hand
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Low cost techniques
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Techniques at a
glance
Don’t double (if you don’t really need it)
Self shunt
Anonymous class
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Don’t double Use real objects when:
• They have no behavior or it is very
simple
• They have no side effects
• They are immutable
• They have no dependencies (or depend
on similar objects)
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Don’t double
$request = new GetObjectsRequest (‘param1’, ‘param2’);
$serviceUnderTest = new Service();
$result = $serviceUnderTest->execute($request);
$this->assertEquals(‘expected’, $result);
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Self-shunt Use the TestCase as double (WTF!)
Great for simple doubles
Great for early stages of TDD
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Self-shunt You will need an interface to double
Make the test double implement interface
You can implement spies
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Self-shunt stub
Class ServiceTest extends TestCase implements GetObjectsRequestInterface
{
public function testSomething()
{
$serviceUnderTest = new Service();
$result = $serviceUnderTest->execute($this);
$this->assertEquals(‘expected’, $result);
}
public function param1()
{
return ‘param1’;
}
public function param2()
{
return ‘param2’;
}
}
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Self-shunt spy
interface CollaboratorInterface
{
public function doThatThing(): string;
}
We will need a collaborator for our service
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Self-shunt spy
class ServiceTest extends TestCase
implements CollaboratorInterface
{
private $collaboratorCalls = 0;
public function testSomething()
{
$serviceUnderTest = new Service($this);
$result = $serviceUnderTest->execute();
$this->assertEquals(‘expected’, $result);
$this->assertEquals(1, $this->collaboratorCalls);
}
public function doThatThing(): string
{
$this->collaboratorCalls+;
return ‘something’;
}
}
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Anonymous
class
Create doubles on the fly
Code exactly what you need
Test Abstract classes
Doesn’t require a framework
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Anonymous
class
Implement interface or subclass
May use builders
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Anonymous class class ServiceTest extends TestCase
{
public function testSomething()
{
$collaborator = new class ()
implements CollaboratorInterface
{
private $calls = 0;
public function doThatThing(): string
{
$this->calls++;
return ‘something’;
}
public function calls()
{
return $this->calls;
}
};
$serviceUnderTest = new Service($collaborator);
$result = $serviceUnderTest->execute();
$this->assertEquals(‘expected’, $result);
$this->assertEquals(1, $collaborator->calls());
}
}
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