Code Contract

Normally we use Debug.Assert() for code contracts. To stop the Debug.Assert() statements from activating during unit tests, add the following to te unit tests application config file ("App.Config"):

  <?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <system.diagnostics>
        <assert assertuienabled="false"/> <!-- Disable Debug.Assert() when running unit tests in debug mode. -->
    </system.diagnostics>
</configuration>

Following is a code contract type class that can make code assertions without throwing an Assert dialog during an NUnit test. Also the code contracts will be logged in release. A potential product failure in the field could be traced back to a code contract failure.

using System;
using System.Diagnostics;
using System.Runtime.CompilerServices;

namespace Common.CodeContracts
{
    /// <summary>
    /// A simple code contract class to replace Debug.Assert(). It can be used in release 
    /// and will log code contract failures to the Trace output window.
    /// </summary>
    public static class RuntimeCodeContract
    {
        // Switch on the Debugger.Break when required
        public static bool DebuggerBreakOnFailure { get; set; } = false;

        public static void Requires(bool condition,
                string message,
                [CallerFilePath] string file = "",
                [CallerMemberName] string member = "",
                [CallerLineNumber] int line = 0)
        {
            if (!condition)
            {
                var msg = $"Code contract failure detected: \"{message}\" in member \"{member}\" on line {line} in file \"{file}\"";
                Trace.TraceError(msg);
                if (DebuggerBreakOnFailure)
                {
                    Debugger.Break(); // Use the call stack window to find the invoker location
                }

                //throw new InvalidOperationException(msg);
            }
        }

        public static void RequiresArgument(bool condition,
                string paramName,
                string message = "",
                [CallerFilePath] string file = "",
                [CallerMemberName] string member = "",
                [CallerLineNumber] int line = 0)
        {
            if (!condition)
            {
                var msg = $"Argument requirement failure detected: {message} \"{paramName}\" in member \"{member}\" on line {line} in file \"{file}\"";
                Trace.TraceError(msg);
                if (DebuggerBreakOnFailure)
                {
                    Debugger.Break(); // Use the call stack window to find the invoker location
                }

                //throw new ArgumentException(message, paramName);
            }
        }

        public static void RequiresArgumentNotNull(object parameter,
                string paramName,
                [CallerFilePath] string file = "",
                [CallerMemberName] string member = "",
                [CallerLineNumber] int line = 0)
        {
            if (parameter == null)
            {
                var msg = $"Argument {paramName} was null in member {member} on line {line} in file {file}";
                Trace.TraceError(msg);
                if (DebuggerBreakOnFailure)
                {
                    Debugger.Break(); // Use the call stack window to find the invoker location
                }

                //throw new ArgumentNullException(msg, paramName);
            }
        }

    }
}

It is also a good example of using the compiler attributes "CallerFilePath", "CallerMemberName", and "CallerLineNumber" for diagnostics.