Mocking with a Closure

[vinkaga]

For the following class

class Demo {
  public function aFunc() {
    return 'initialFunc';
  }
}

I have written the following test that mocks the class replacing aFunc with a closure as follows

class DemoTest extends PHPUnit_Framework_TestCase {
  public function testWithClosure() {
    \AspectMock\Test::double(Demo::class, [
      'aFunc' => function($a) { return $a.$a; },
    ]);
    $mockDemo = new Demo();
    $this->assertEquals('abcabc', $mockDemo->aFunc('abc'));
  }
}

When I run it, I get the following error

$ ../vendor/bin/phpunit .
PHPUnit 4.8.35 by Sebastian Bergmann and contributors.

E

Time: 222 ms, Memory: 7.25MB

There was 1 error:

1) DemoTest::testWithClosure
Missing argument 1 for Demo::{closure}()

dev/ez-mock/test/DemoTest.php:10
dev/ez-mock/vendor/codeception/aspect-mock/src/AspectMock/Core/Mocker.php:154
dev/ez-mock/vendor/codeception/aspect-mock/src/AspectMock/Core/Mocker.php:79
dev/ez-mock/vendor/codeception/aspect-mock/src/AspectMock/Core/Mocker.php:28
dev/ez-mock/vendor/codeception/aspect-mock/src/AspectMock/Intercept/before_mock.php:3
dev/ez-mock/test/Demo.php:4
dev/ez-mock/test/DemoTest.php:13

FAILURES!
Tests: 1, Assertions: 0, Errors: 1.

What am I doing wrong?