Limits text to a certain maximum length for the purpose of showing it to the user as part of some (G)UI or report that has limited space.

/// <summary>Limit the text length</summary>
/// <param name="text">Text to limit</param>
/// <param name="maxLength">Maximum allowed number of characters
/// in the result</param>
/// <param name="showEllipsis"><code>true</code>=Limit
/// <paramref name="text"/> to first
/// (<paramref name="maxLength"/>-3) characters plus "...",
/// <code>false</code>=Limit <paramref name="text"/> to first
/// <paramref name="maxLength"/> characters</param>
/// <returns>Content of <paramref name="text"/>, but at most
/// <paramref name="maxLength"/> characters</returns>
/// <remarks>With <paramref name="showEllipsis"/> left to default
/// value of <code>true</code> the result will be "..." even if
/// you specify a maximum length less than or equal to 3.</remarks>
public static string LimitTextLength(this string text, int maxLength, bool showEllipsis = true)
{
        if (maxLength < 0)
        {
            throw new ArgumentOutOfRangeException("maxLength", "Value must not be negative");
        }
        if (string.IsNullOrWhiteSpace(text))
        {
            return string.Empty;
        }

        var n = text.Length;
        var ellipsis = showEllipsis ? "..." : string.Empty;
        var minLength = ellipsis.Length;
        maxLength = Math.Max(minLength, maxLength);

        return n > maxLength ? text.Substring(0, Math.Min(maxLength - minLength, n)) + ellipsis : text;
}

[TestMethod]
public void LimitTextLength_null()
{
    foreach (var n in Enumerable.Range(0, 10))
    {
        ((string)null).LimitTextLength(n).Should().BeEmpty();
    }
}

[TestMethod]
public void LimitTextLength_empty()
{
    foreach (var n in Enumerable.Range(0, 10))
    {
        string.Empty.LimitTextLength(n).Should().BeEmpty();
    }
}

[TestMethod]
[ExpectedException(typeof(ArgumentOutOfRangeException))]
public void LimitTextLength_negative_length()
{
    "test".LimitTextLength(-1);
}

[TestMethod]
public void LimitTextLength_cut_off_yes_ellipsis_default()
{
    "abcdefg".LimitTextLength(6).Should().Be("abc...");
}

[TestMethod]
public void LimitTextLength_cut_off_yes_ellipsis_no()
{
    "abcdefg".LimitTextLength(6, false).Should().Be("abcdef");
}

[TestMethod]
public void LimitTextLength_cut_off_yes_ellipsis_yes()
{
    "abcdefg".LimitTextLength(6, true).Should().Be("abc...");
}

[TestMethod]
public void LimitTextLength_cut_off_edge()
{
    "abcdefg".LimitTextLength(7).Should().Be("abcdefg");
}

[TestMethod]
public void LimitTextLength_cut_off_no()
{
    "abcdefg".LimitTextLength(8).Should().Be("abcdefg");
}

[TestMethod]
public void LimitTextLength_almost_ellipsis_length()
{
    "abcdefg".LimitTextLength(4, true).Should().Be("a...");
}

[TestMethod]
public void LimitTextLength_exactly_ellipsis_length()
{
    "abcdefg".LimitTextLength(3, true).Should().Be("...");
}

[TestMethod]
public void LimitTextLength_shorter_than_ellipsis()
{
    "abcdefg".LimitTextLength(2, true).Should().Be("...");
}