phpunit - mockbuilder - set mock object internal property

You can make the property public by using Reflection, and then set the desired value:

$a = new A;
$reflection = new ReflectionClass($a);
$reflection_property = $reflection->getProperty('p');
$reflection_property->setAccessible(true);

$reflection_property->setValue($a, 2);

Anyway in your example you don't need to set p value for the Exception to be raised. You are using a mock for being able to take control over the object behaviour, without taking into account it's internals.

So, instead of setting p = 2 so an Exception is raised, you configure the mock to raise an Exception when the blah method is called:

$mockA = $this->getMockBuilder('A')
        ->disableOriginalConstructor()
        ->getMock();
$mockA->expects($this->any())
         ->method('blah')
         ->will($this->throwException(new Exception));

Last, it's strange that you're mocking the A class in the ATest. You usually mock the dependencies needed by the object you're testing.

Hope this helps.

Based on the accepted answer from @gontrollez, since we are using a mock builder we do not have the need to call new A; since we can use the class name instead.

    $a = $this->getMockBuilder(A::class)
        ->disableOriginalConstructor()
        ->getMock();

    $reflection = new ReflectionClass(A::class);
    $reflection_property = $reflection->getProperty('p');
    $reflection_property->setAccessible(true);

    $reflection_property->setValue($a, 2);

Based on @rsahai91 answer above, created a new helper for making multiple methods accessible. Can be private or protected

/**
 * Makes any properties (private/protected etc) accessible on a given object via reflection
 *
 * @param $object - instance in which properties are being modified
 * @param array $properties - associative array ['propertyName' => 'propertyValue']
 * @return void
 * @throws ReflectionException
 */
public function setProperties($object, $properties)
{
    $reflection = new ReflectionClass($object);
    foreach ($properties as $name => $value) {
        $reflection_property = $reflection->getProperty($name);
        $reflection_property->setAccessible(true);
        $reflection_property->setValue($object, $value);
    }
}

Example use:

$mock = $this->createMock(MyClass::class);

$this->setProperties($mock, [
    'propname1' => 'valueOfPrivateProp1',
    'propname2' => 'valueOfPrivateProp2'
]);

Thought i'd leave a handy helper method that could be quickly copy and pasted here:

/**
 * Sets a protected property on a given object via reflection
 *
 * @param $object - instance in which protected value is being modified
 * @param $property - property on instance being modified
 * @param $value - new value of the property being modified
 *
 * @return void
 */
public function setProtectedProperty($object, $property, $value)
{
    $reflection = new ReflectionClass($object);
    $reflection_property = $reflection->getProperty($property);
    $reflection_property->setAccessible(true);
    $reflection_property->setValue($object, $value);
}