public function checkCompleted(): ?EventCollection
    {
        $cardinality = $this->resetCardinality()->assertSingular();
        $endEvent = $this->call->endEvent();

        list($matchCount, $matchingEvents) =
            $this->matchIf($endEvent, $endEvent);

        if ($cardinality->matches($matchCount, 1)) {
            return $this->assertionRecorder->createSuccess($matchingEvents);
        }

        return null;
    }