Changes needed so ICommandHandler classes are testable

[dougclutter]

I'm using Beta 2, so please excuse (ignore) me if this has already been addressed.

The ICommandHandler.InvokeAsync method takes an InvocationContext parameter. Unfortunately, I couldn't find a way to instantiate an InvocationContext in my unit tests, so I couldn't suss out how to test it...

Perhaps, this parameter could be changed to an interface?

[jonsequitur]

You can do this:

var command = new RootCommand();
command.SetHandler((InvocationContext ctx) => ctx.Console.Out.Write("hello!"));
var testConsole = new TestConsole();
var parseResult = command.Parse();
var context = new InvocationContext(parseResult, testConsole);
await command.Handler.InvokeAsync(context);
// check output using testConsole.Out.ToString()

In practice though, this is simpler:

var command = new RootCommand();
command.SetHandler((InvocationContext ctx) => ctx.Console.Out.Write("hello!"));
var testConsole = new TestConsole();
await command.InvokeAsync("", testConsole);
// check output using testConsole.Out.ToString()