[ 測試撰寫 ] LeetCode 141. Linked List Cycle

[LPenny-github]

相關 Discussions:
#121

LeetCode:
https://leetcode.com/problems/linked-list-cycle/

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其實不知道該怎麼測試 😅，所以我寫了一個方法去驗證是否為 valid index
再麻煩 @twy30 給予 測試撰寫的建議 orz 感激不盡

using Xunit;

public class UnitTestLinkedListCycle
{
    bool IsValidCycleIndex(int[] nodeValue, int cycleIndex)
    {
        if (cycleIndex == -1) { return false; }
        int count = 0;
        while (count < nodeValue.Length)
        {
            if (count == cycleIndex)
            {
                return true;
            }
            ++count;
        }
        return false;
    }
    [Fact]
    public void LeetCodeExample1()
    {
        var node1 = new ListNode(3);
        var node2 = new ListNode(2);
        var node3 = new ListNode(0);
        var node4 = new ListNode(-4);
        node1.next = node2;
        node2.next = node3;
        node3.next = node4;
        node4.next = node2;
        Assert.Equal(IsValidCycleIndex(new int[] { 3, 2, 0, -4 }, 1), 
                                                  new LinkedListCycle().HasCycle(node1));
    }
    [Fact]
    public void LeetCodeExample2()
    {
        var node1 = new ListNode(1);
        var node2 = new ListNode(2);
        node1.next = node2;
        node2.next = node1;
        Assert.Equal(IsValidCycleIndex(new int[] { 1, 2 }, 0), 
                                                  new LinkedListCycle().HasCycle(node1));
    }
    [Fact]
    public void LeetCodeExample3()
    {
        var node1 = new ListNode(1);
        Assert.Equal(IsValidCycleIndex(new int[] { 1 }, -1), 
                                                  new LinkedListCycle().HasCycle(node1));
    }
    [Fact]
    public void maxNodeValue()
    {
        var node1 = new ListNode(100000);
        var node2 = new ListNode(1000);
        var node3 = new ListNode(10);
        node1.next = node2;
        node2.next = node3;
        node3.next = node3;
        Assert.Equal(IsValidCycleIndex(new int[] { 100000, 1000, 10 }, 2), 
                                                  new LinkedListCycle().HasCycle(node1));
    }
    [Fact]
    public void minNodeValue()
    {
        var node1 = new ListNode(-100000);
        var node2 = new ListNode(-10);
        var node3 = new ListNode(0);
        var node4 = new ListNode(2);
        node1.next = node2;
        node2.next = node3;
        node3.next = node4;
        node4.next = node4;
        Assert.Equal(IsValidCycleIndex(new int[] { -100000, -10, 0, 2 }, 3), 
                                                  new LinkedListCycle().HasCycle(node1));
    }
}

[twy30]

@LPenny-github

你好 😊

你有把 LeetCode 給的 3 組範例的「 setup (建置測試資料) 」的部分寫得很好，最後的「 Assert (驗證) 」的部分可以改成以下這樣：

    public void LeetCodeExample1()
    {
        // ...

        Assert.Equal(true, new LinkedListCycle().HasCycle(node1));
    }

    [Fact]
    public void LeetCodeExample2()
    {
        // ...

        Assert.Equal(true, new LinkedListCycle().HasCycle(node1));
    }
    [Fact]
    public void LeetCodeExample3()
    {
        // ...

        Assert.Equal(false, new LinkedListCycle().HasCycle(node1));
    }

就這題的情形來說，「選擇具有代表性的測試案例，直接 hard-code 期待值，與 實際值 比對」是比較適當的作法。

---

比較完整的觀念可以參考 https://martinfowler.com/articles/mocksArentStubs.html

• Dummy objects are passed around but never actually used. Usually they are just used to fill parameter lists.
• Fake objects actually have working implementations, but usually take some shortcut which makes them not suitable for production (an in memory database is a good example).
• Stubs provide canned answers to calls made during the test, usually not responding at all to anything outside what's programmed in for the test.
• Spies are stubs that also record some information based on how they were called. One form of this might be an email service that records how many messages it was sent.
• Mocks are what we are talking about here: objects pre-programmed with expectations which form a specification of the calls they are expected to receive.

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這題的重點在於「 cycle 的有無」，而「每個節點的值」的影響就相對的小很多；若是我，我會拿掉 maxNodeValue() 與 minNodeValue()

[LPenny-github]

比較完整的觀念可以參考 https://martinfowler.com/articles/mocksArentStubs.html

這個部分，以我目前的程度很難立即消化，我會慢慢看。

謝謝 @twy30 大大 orz