Moved analyzer tests to its own project

Also moves tests to `./test` which makes it possible
for all test projects to share the same .editorconfig
files and similar.

test/Spectre.Console.Tests/Utilities/Extensions/CommandContextExtensions.cs

@@ -0,0 +1,30 @@
+using System;
+using System.Linq;
+using Shouldly;
+
+namespace Spectre.Console.Cli
+{
+    public static class CommandContextExtensions
+    {
+        public static void ShouldHaveRemainingArgument(this CommandContext context, string name, string[] values)
+        {
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
+            if (values == null)
+            {
+                throw new ArgumentNullException(nameof(values));
+            }
+
+            context.Remaining.Parsed.Contains(name).ShouldBeTrue();
+            context.Remaining.Parsed[name].Count().ShouldBe(values.Length);
+
+            foreach (var value in values)
+            {
+                context.Remaining.Parsed[name].ShouldContain(value);
+            }
+        }
+    }
+}