PhpUnit does not identify TypeError with string numbers and Abstract Class - phpunit

Question

With the following class
declare(strict_types=1);
abstract class IntValueObject
{
public function __construct(protected int $value)
{
}
}
and the test
declare(strict_types=1);
final class IntValueObjectTest extends TestCase
{
public function testWithNotValidValue(): void
{
$value = '1';
$this->expectException(\TypeError::class);
$this->getMockForAbstractClass(IntValueObject::class, [$value]);
}
}
return
Api\Tests\Shared\Domain\ValueObject\IntValueObjectTest::testWithNotValidValue
Failed asserting that exception of type "TypeError" is thrown.
If I change $value from '1' to 'foo' if it passes the test.
We use PHP 8, and in production, if the value '1' is passed it would give TypeError, why doesn't this happen in the test?
Thanks in advance.
ORIGIN OF THE "PROBLEM"
https://bugs.php.net/bug.php?id=81258
POSSIBLE SOLUTION
declare(strict_types=1);
final class IntValueObjectTest extends TestCase
{
public function testWithNotValidValue(): void
{
$value = '1';
$this->expectException(\TypeError::class);
new class($value) extends IntValueObject {};
}
}

Answer 1

One explanation I can imagine is that during the test, IntValueObject::__construct('1') is called from code that is not using declare(strict_types=1); and therefore the string '1' is being coerced to integer 1. No TypeError is thrown in that case (but it would for string 'foo' - as you describe the behaviour in your question).
The Cause
The cause is using a generated mock:
<?php declare (strict_types = 1);
...
$this->expectException(\TypeError::class);
$this->getMockForAbstractClass(IntValueObject::class, [$value]);
...
To not have a TypeError in this situation is likely unexpected to you as you have scalar strict types but still see the type-coercion of the string '1' to integer 1 for the constructors' first parameter.
The Mismatch
However the TypeError is only thrown when the code calling IntValueObject::__construct(int $value) has declare(strict_types=1).
While the test-code has declare(strict_types=1) it must not be that code where the constructor method is called - as no TypeError is thrown.
For Real
Behind the scenes $this->getMockForAbstractClass(...); uses an Instantiator from the Doctrine project which is making use of PHP reflection (meta-programming). As those methods are all internal code, declare(strict_types=1) is not effective and there is no TypeError anymore.
Compare with the following code-example:
<?php declare(strict_types=1);
class Foo {
public function __construct(int $integer) {
$this->integer = $integer;
}
}
try {
$foo = new Foo('1');
} catch (TypeError $e) {
} finally {
assert(isset($e), 'TypeError was thrown');
assert(!isset($foo), '$foo is unset');
}
$foo = (new ReflectionClass(Foo::class))->newInstance('1');
var_dump($foo);
When executed with assertions enabled, the output is the following:
object(Foo)#3 (1) {
["integer"]=>
int(1)
}
Within the try-block, the TypeError is thrown with new as you expect it.
But afterwards when instantiating with PHP reflection it is not.
(see as well https://3v4l.org/aZTJl)
The Remedy
Add a class to your test-suite that is really mocking the abstract base class and place it next to the test of it so you can easily use it:
<?hpp declare(strict_types=1);
class IntValueObjectMock extends IntValueObject
{...}
Then use IntValueObjectMock in your test:
$value = '1';
$this->expectException(\TypeError::class);
new IntValueObjectMock($value);
Alternatively use anonymous class when extending it is straight forward:
$value = '1';
$this->expectException(\TypeError::class);
new class($value) extends IntValueObject {};
Or apply type-checks on the constructor method your own, either with PHP reflection or run static code-analysis which has the benefit that it can detect such issues already without instantiating - so no additional test-code is involved.