我正在尝试使用PHPUnit在Laravel中编写我的第一个单元测试。我正在编写的测试试图验证一个相当简单的helper函数是否正常工作。编写它的方式是，我的函数需要一个或两个参数，然后尝试验证参数是否合适;换句话说，如果函数在为参数提供的特定值上抛出InvalidArgumentException，那么函数就可以正常工作。
如何编写一个单元测试，实际上，如果函数在第二个参数中得到一个十进制数，而它需要的是一个int（或者提供了一个int，但它超出了范围），则应该抛出InvalidArgumentException？Assert应该是什么样子的？（我看了可用Assert的列表，但没有任何东西适合异常。）
以下是我的全部职能：

namespace App\Helpers;

/**
 * This class contains a variety of helper functions useful to this app.
 */
class Helper2
{
    /**
     * This function chooses a random number of elements from an array and chooses
     * them at random.
     *
     * $array - the array of items from which elements will be selected
     * $numberOfElements - the number of elements from the array that the user desires.
     *
     * The array needs to be a simple array of strings, integers, etc.
     *
     * The $numberOfElements defaults to null. When the value is null, the function
     * will choose a random number of elements between 1 and the number of elements
     * in the array. If a non-null value greater than 0 is provided, that number of
     * elements will be returned by the function. If the number is larger than the
     * number of elements in the array, all elements of the array will be returned.
     */
    public static function choose_random_elements(array $array, int $numberOfElementsDesired = null)
    {
        // The first argument of the function must be an array. (No test necessary:
        // Laravel will not even let you code the function call with anything but
        // an array in the first argument.)
         /*    if (! is_array($array)) {
            throw new \InvalidArgumentException("The input array is not actually an array.");
        }
         */
        // Store the array in a collection.
        $myCollection = collect($array);

        // The second argument of the function must be numeric.
        if (! is_numeric($numberOfElementsDesired)) {
            throw new \InvalidArgumentException ("The number of elements desired must be a number.");
        }

        // The second argument of the function must be an integer.
        if (! is_integer($numberOfElementsDesired)) {
            throw new \InvalidArgumentException ("The number of elements desired must be an integer.");
        }

        // The second argument of the function cannot exceed the number of elements in the array.
        if ($numberOfElementsDesired > count($myCollection)) {
            throw new \InvalidArgumentException ("The number of elements desired cannot exceed the number of elements in the array.");
        }

        // The second argument of the function cannot be zero or less.
        if ($numberOfElementsDesired <= 0) {
            throw new \InvalidArgumentException("You cannot choose a negative number of elements from the array.");
        }

        // If no value was supplied for the second argument of the function, choose
        // an integer between 1 and the number of elements in the array.
        if (is_null($numberOfElementsDesired)) {
            $numberOfElementsDesired = rand(1, count($myCollection));
        }

        // If the number supplied for the second argument of the function exceeds
        // the number of elements in the array, set the second argument to the size
        // of the array.
        if ($numberOfElementsDesired > count($myCollection)) {
            $numberOfElementsDesired = count($myCollection);
        }

        // Choose a random number of elements at random from the collection and put them in a new collection.
        $randomSelectionsCollection = $myCollection->random($numberOfElementsDesired);

        // Convert the resulting collection into an array.
        $randomSelectionsArray = $randomSelectionsCollection->toArray();

        // Convert the array of selected elements into a string.
        $randomSelectionsString = implode(',', $randomSelectionsArray);

        echo "Function output: " . $randomSelectionsString . "\n";

        return $randomSelectionsString;
    }
}

我能想到的唯一替代方法是在try/catch块中编写测试。我想到了这个方法，而且看起来很有效。这是编写这种测试的合理方法还是有更好的方法？

try {
    $result = $helper2->choose_random_elements(array(1, 6, "cat"), -4);
} catch(InvalidArgumentException $excp) {
    $this->assertEquals("You cannot choose a negative number of elements from the array.", $excp->getMessage());
}

我正在运行拉勒维9号。