Sokil\Mongo\CollectionTest::testDeleteDocuments_WrongExpressionSpecified PHP Method

    public function testDeleteDocuments_WrongExpressionSpecified()
    {
        // add
        $this->collection->createDocument(array('param' => 1))->save();
        $this->collection->createDocument(array('param' => 2))->save();
        $this->collection->createDocument(array('param' => 3))->save();
        $this->collection->createDocument(array('param' => 4))->save();
        // delete
        $this->collection->deleteDocuments('hello');
    }