public function invocations(string $method): Invocations
    {
        if (empty($method)) {
            throw new \InvalidArgumentException(
                    'Please provide a method name to retrieve invocations for.'
            );
        }

        if (!isset($this->_allowedMethods[$method])) {
            throw new \InvalidArgumentException(
                    $this->canNot('retrieve invocations for', $method)
            );
        }

        if (!isset($this->invocations[$method])) {
            $this->invocations[$method] = new Invocations(
                    $this->completeNameOf($method),
                    $this->_methodParams[$method]
            );
        }

        return $this->invocations[$method];
    }