public static void Insert_Char_Invalid()
{
var builder = new StringBuilder(0, 5);
builder.Append("Hello");
Assert.Throws<ArgumentOutOfRangeException>("index", () => builder.Insert(-1, '\0')); // Index < 0
Assert.Throws<ArgumentOutOfRangeException>("index", () => builder.Insert(builder.Length + 1, '\0')); // Index > builder.Length
Assert.Throws<ArgumentOutOfRangeException>("requiredLength", () => builder.Insert(builder.Length, '\0')); // New length > builder.MaxCapacity
}