Add FakeCommandHandler for testing ICommandHandler implementations

Author: MarkDerman

Patterns/CommandHandler/FakeCommandHandler.cs

@@ -0,0 +1,59 @@
+namespace Odin.Patterns.CommandHandler;
+
+/// <summary>
+/// Generic treatment of ICommandHandler for use in testing and other scenarios.
+/// </summary>
+/// <typeparam name="TCommand"></typeparam>
+public class FakeCommandHandler<TCommand>  : ICommandHandler<TCommand> 
+    where TCommand : ICommand
+{
+    /// <summary>
+    /// Default constructor. 
+    /// </summary>
+    public FakeCommandHandler()
+    {
+        
+    }
+    
+    /// <summary>
+    /// Does nothing.
+    /// </summary>
+    /// <param name="command"></param>
+    /// <param name="ct"></param>
+    /// <exception cref="NotImplementedException"></exception>
+    public virtual async Task HandleAsync(TCommand command, CancellationToken ct = default)
+    {
+        await Task.CompletedTask;
+    }
+}
+
+/// <summary>
+/// Does not do anything.
+/// </summary>
+/// <typeparam name="TCommand"></typeparam>
+/// <typeparam name="TResult"></typeparam>
+public class FakeCommandHandler<TCommand, TResult>  : ICommandHandler<TCommand, TResult>  
+    where TCommand : ICommand<TResult>
+{
+    private readonly TResult _resultToReturn;
+    
+    /// <summary>
+    /// Initialise to return 'result' on HandleAsync.
+    /// </summary>
+    /// <param name="result"></param>
+    public FakeCommandHandler(TResult result)
+    {
+        _resultToReturn = result;
+    }
+    
+    /// <summary>
+    /// Does nothing.
+    /// </summary>
+    /// <param name="command"></param>
+    /// <param name="ct"></param>
+    /// <exception cref="NotImplementedException"></exception>
+    public async Task<TResult> HandleAsync(TCommand command, CancellationToken ct = default)
+    {
+        return await Task.FromResult(_resultToReturn);
+    }
+}