许多测试用例都涵盖了一个函数phpunit

对于下面的函数，我需要写更多的测试用例，我已经写了一个，有人能给出一些想法吗，也许是为了测试中间函数调用的返回值。

 public function calculateShortestPath($graphObj, $start, $destination)
{
    $shortestPath = null;
    if ($this->validateParams($graphObj, $start, $destination) == true) {
        $result = $this->getAllVerticesAndNeighbours($graphObj);
        $vertices = $result[self::VERTICES];
        $neighbours = $result[self::NEIGHBOURS];
        $vertexCost = array_fill_keys($vertices, self::INFINITY);
        $visitedVertices = array_fill_keys($vertices, null);
        $vertexCost[$start] = 0;
        $vertexQueue = $vertices;
        $result = $this->getShortestPath($vertexQueue, $vertexCost, $neighbours, $visitedVertices, $destination);
        $vertexCost = $result[self::VERTEX_COST];
        $shortestPathVertices = $result[self::SHORTEST_PATH_VERTICES];
        $path = $this->getRefinedShortestPath($shortestPathVertices, $destination);
        $shortestPath = new ShortestPath($path, $vertexCost[$destination]);
    }
    return $shortestPath;
}

我已经写了以下案例，

 /**
 * Test for calculateShortestPath function
 *
 * @param string|int $start starting point
 * @param string|int $destination destination point
 * @param array $expectedShortestPath expected shortest path
 * @param int|float $expectedCost expected cost
 * @dataProvider testCalculateShortestPathDataProvider
 */
public function testCalculateShortestPath($start, $destination, $expectedShortestPath, $expectedCost)
{
    $actualResult = $this->shortestPathCalc->calculateShortestPath($this->graph, $start, $destination);
    /* @var $actualResult ShortestPath */
    $this->assertEquals(
        $expectedShortestPath,
        $actualResult->getPath(),
        sprintf('Incorrect shortest path from %d to %d !', $start, $destination)
    );
    $this->assertEquals(
        $expectedCost,
        $actualResult->getCost(),
        sprintf('Incorrect shortest path cost from %d to %d !', $start, $destination)
    );
}