PhpDeal\Functional\Invariant\ContractTest::testInvariantViolatedAfterSeveralMethods PHP Method

    public function testInvariantViolatedAfterSeveralMethods()
    {
        $this->stub->accelerate(10, 30);
        // let's have a speed 300m/s
        $this->stub->decelerate(20, 20);
        // Negative speed?
    }