String Comparison Unit Test Helper

TestHelper.cs

public static class StringTestHelpers
{
	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.Equal(expectedValue, actualValue);
			return;
		}

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

		output.WriteLine("Position\t Expected  \t Actual");
		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,-3}{1}\t  {2,-4} ({3,-3})\t {4,-4} ({5,-3})",
					                i, // the index
					                i < minLen && actualValue[i] == expectedValue[i] ? " " : "*",		// put a mark beside a differing row
									i < expectedValue.Length ? expectedValue[i].ToSafeString() : "",	// character safe string
									i < expectedValue.Length ? HexChar(expectedValue[i]) : "",			// character decimal value
					                i < actualValue.Length ? actualValue[i].ToSafeString() : "",		// character safe string
					                i < actualValue.Length ? (HexChar(actualValue[i])) : ""				// character decimal value
					);
			}
		}
		output.WriteLine();
		output.Close();

		Assert.Equal(expectedValue, actualValue);
	}

	private static string HexChar(char c)
	{
		var num = (int) c;
		return string.Format(@"\u{0:X4}", num);
	}

	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";
				case '\u0020':
					return @"\s";
				default:
					return String.Format(@"\u{0:X};", (int) c);
			}
		}
		return c.ToString(CultureInfo.InvariantCulture);
	}

	public enum DiffStyle
	{
		Full,
		Minimal
	}
}