How can I write TDD code from the code below?

Question

static void Main(string[] args)
{
    for (int i =1 ; i<=100;i++)
    {
        Console.WriteLine(i.ToString());

        if (i % 3 == 0)
            Console.WriteLine("HOON");
        if (i % 5 == 0)
            Console.WriteLine("Group");
        if (i % 3 == 0 && i % 5 == 0)
            Console.WriteLine("HOON Group");
    }
}

I need to write test code using the above code.

There are three features. Anyone could you advise me please?

[TestClass]
public class UnitTest1
{
    [TestMethod]
    public void TestMethod1()
    {
    }
}

Is this Fizz Buzz's new name? – GazTheDestroyer Mar 04 '14 at 09:19 — GazTheDestroyer, Mar 04 '14 at 09:19
Shouldn't this be tagged `homework` or `interview`? – Albireo Mar 04 '14 at 09:38 — Albireo, Mar 04 '14 at 09:38

score 12 · Answer 1 · edited May 23 '17 at 12:28

You cannot write Test-Driven Code from existing code, because tests should be written before you write implementation.

Simplest way of testing your code is providing TextWriter mock to Console.Out and verifying generated output.

UPDATE: If you want to use TDD, then you should modify your code to make it testable. Here your Program class does to many things - it is responsible both for presentation (output results to console) and business logic (calculating of values). For testing business logic you should move this functionality to separate class.

Lets start. First test:

[Test]
public void ShoulReturnHoonWhenValueDivisibleOnlyBy3()
{
    var hoonGroup = new HoonGroup();
    string result = hoonGroup.Calculate(3);
    Assert.AreEqual("HOON", result);
}

It fails to compile, because you don't have HoonGroup class. Create class, create method Calculate. Make code compilable:

public class HoonGroup
{
    public string Calculate(int value)
    {
        return "";
    }
}

Now your test fails because you are returning empty string. Just hard-code "HOON" to make test pass. Thats OK with TDD.

public class HoonGroup
{
    public string Calculate(int value)
    {
        return "HOON";
    }
}

Next test:

[Test]
public void ShoulReturnGroupWhenValueDivisibleOnlyBy5()
{
    var hoonGroup = new HoonGroup();
    string result = hoonGroup.Calculate(5);
    Assert.AreEqual("Group", result);
}

Of course, test fails. Update implementation:

public class HoonGroup
{
    public string Calculate(int value)
    {
        return (value == 5) ? "Group" : "HOON";
    }
}

Looks stupid. But it implements all requirements of your code. Another test:

[Test]
public void ShoulReturnNullWhenValueIsNotDivisibleBy3Or5()
{
    var hoonGroup = new HoonGroup();
    string result = hoonGroup.Calculate(5);
    Assert.IsNull(result);
}

No problem - add another condition:

public class HoonGroup
{
    public string Calculate(int value)
    {
        if (value == 3)
            return "HOON";

        if (value == 5)
            return "Group";

        return null;
    }
}

Tests pass. We need more test cases. It's easy to do with NUnit - just decorate first test with TestCase attributes (MSTest also has similar feature):

[TestCase(3)]
[TestCase(6)]
[TestCase(99)]
public void ShoulReturnHoonWhenValueDivisibleOnlyBy3(int value)
{
    var hoonGroup = new HoonGroup();
    string result = hoonGroup.Calculate(value);
    Assert.AreEqual("HOON", result);
}

And now its easier to create code which checks if value is divisible by 3 then listing all possible values:

public class HoonGroup
{
    public string Calculate(int value)
    {
        if (value % 3 == 0)
            return "HOON";

        if (value == 5)
            return "Group";

        return null;
    }
}

I think you get the point and rithm of TDD. Create more test cases for values divisible by 5 and write test for values divisible both by 3 and 5.

Thank you for your comment, If I assume that I know what should I write in here and I want to write test first, can you add simple example for the above logic please? — Joel Park, Mar 04 '14 at 09:32

score 1 · Answer 2 · answered Mar 04 '14 at 09:30

Rewrite your code to make it testable.

BTW, it looks wrong, so I would write it like this:

static void Main(string[] args)
{
    for (int i =1 ; i<=100;i++)
    {
        Console.WriteLine(i.ToString());

        var name = GetName(i);
        if (name != null)
        {
            Console.WriteLine(name);
        }
    }
}

internal static string GetName(int i)
{
    if (i % 3 == 0)
    {
        if (i % 5 == 0)
        {
            return "HOON Group";
        }
        else
        {            
            return "HOON";
        }
    }
    else if (i % 5 == 0)
    {
        return "Group";
    }
    else
    {
        return null;
    }
}

Now the GetName function is testable.

A test might look like this:

[TestMethod]
public void TestMethod1()
{
    Assert.AreEqual("Hoon Group", Program.GetName(15));
    Assert.AreEqual("Hoon", Program.GetName(3));
    Assert.AreEqual("Group", Program.GetName(5));

    // test other values here
}

This example assumes that you have use the InternalsVisibleToAttribute. If not, make GetName public. For more information, see http://msdn.microsoft.com/en-us/library/system.runtime.compilerservices.internalsvisibletoattribute.aspx

score 0 · Answer 3 · answered Mar 04 '14 at 09:56

0

If you are interested, this is how you could solve FizzBuzz (which is essentially the same problem) using TDD.

http://chilliandrew.blogspot.com/2013/12/tdd-so-whats-this-test-first-thing.html

answered Mar 04 '14 at 09:56

Andrew

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How can I write TDD code from the code below?

3 Answers3