String Comparison Unit Test Helper

TestHelper.cs

public static class TestHelpers
{
    public static void ShouldEqualWithDiff(this string actualValue, string expectedValue)
    {
        ShouldEqualWithDiff(actualValue, expectedValue, DiffStyle.Full, Console.Out);
    }

    public static void ShouldEqualWithDiff(this string actualValue, string expectedValue, DiffStyle diffStyle)
    {
        ShouldEqualWithDiff(actualValue, expectedValue, diffStyle, Console.Out);
    }

    public static void ShouldEqualWithDiff(this string actualValue, string expectedValue, DiffStyle diffStyle, TextWriter output)
    {
        if(actualValue == null || expectedValue == null)
        {
            //Assert.AreEqual(expectedValue, actualValue);
            Assert.Equal(expectedValue, actualValue);
            return;
        }

        if (actualValue.Equals(expectedValue, StringComparison.Ordinal)) return;

        output.WriteLine("  Idx Expected  Actual");
        output.WriteLine("-------------------------");
        int maxLen = Math.Max(actualValue.Length, expectedValue.Length);
        int minLen = Math.Min(actualValue.Length, expectedValue.Length);
        for (int i = 0; i < maxLen; i++)
        {
            if (diffStyle != DiffStyle.Minimal || i >= minLen || actualValue[i] != expectedValue[i])
            {
                output.WriteLine("{0} {1,-3} {2,-4} {3,-3}  {4,-4} {5,-3}",
                    i < minLen && actualValue[i] == expectedValue[i] ? " " : "*", // put a mark beside a differing row
                    i, // the index
                    i < expectedValue.Length ? ((int)expectedValue[i]).ToString() : "", // character decimal value
                    i < expectedValue.Length ? expectedValue[i].ToSafeString() : "", // character safe string
                    i < actualValue.Length ? ((int)actualValue[i]).ToString() : "", // character decimal value
                    i < actualValue.Length ? actualValue[i].ToSafeString() : "" // character safe string
                );
            }
        }
        output.WriteLine();

        //Assert.AreEqual(expectedValue, actualValue);
        Assert.Equal(expectedValue, actualValue);
    }

    private static string ToSafeString(this char c)
    {
        if (Char.IsControl(c) || Char.IsWhiteSpace(c))
        {
            switch (c)
            {
                case '\r':
                    return @"\r";
                case '\n':
                    return @"\n";
                case '\t':
                    return @"\t";
                case '\a':
                    return @"\a";
                case '\v':
                    return @"\v";
                case '\f':
                    return @"\f";
                default:
                    return String.Format("\\u{0:X};", (int)c);
            }
        }
        return c.ToString(CultureInfo.InvariantCulture);
    }
}

public enum DiffStyle
{
    Full, 
    Minimal
}

Moved the Math.Max() outside the loop declaration: https://gist.github.com/1610860

Not knowing C#, I learned with your example the meaning of the prefix @ before a string literal in C# = no escaped char sequences.

@jarshwah Thanks! Are you sure that makes a difference? There are many cases where the C# compiler can optimize calls like this. For example, since it knows that actualValue and expectedValue don't change, it can evaluate the length and max once. I don't know if it does it in this particular case, but would be interesting to check the IL and measure it to see if it really does make a difference. :)

I forked and made some modifications to your snippet, here it is: https://gist.github.com/1615334

• Extended the list of safe strings according to: http://sinairv.wordpress.com/2010/08/08/code-snippet-representing-strings-with-all-their-characters-visible/
• Moved all tabular formatting to the main method using String.Format
• added support for minimal diff representation
• checked for null input strings
• and a little more

PS. how can I send a pull request for a gist?

@sinairv thanks! I'll take a look at it. Unfortunately, gistts don't support pull requests.

@haacked & @sinairv, for readability, I would suggest removing the call to string.Format & using the overload output.WriteLine(string format, params object[] args)

output.WriteLine("{0} {1,-3} {2,-4} {3,-3}  {4,-4} {5,-3}",
    i < minLen && actual[i] == expected[i] ? " " : "*", // put a mark beside a differing row
    i, // the index
    i < expected.Length ? ((int)expected[i]).ToString() : "", // character decimal value
    i < expected.Length ? expected[i].ToSafeString() : "", // character safe string
    i < actual.Length ? ((int)actual[i]).ToString() : "", // character decimal value
    i < actual.Length ? actual[i].ToSafeString() : "" // character safe string
);

@dotnetzebra good suggestion. I made the change.

Thx man.
This helper class help me A LOT with some tricky tests.

I like this. Helped me out a lot.

Maybe consider creating a NuGet package just for this source file. You can create NuGet packages for source pretty easily. I am doing just that now with common files I used to drag around.
http://www.rhyous.com/2016/03/03/nuget-for-source-using-add-as-link-1