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/Unit/ColumnsTests.cs

@@ -0,0 +1,48 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using Spectre.Console.Testing;
+using Spectre.Verify.Extensions;
+using VerifyXunit;
+using Xunit;
+
+namespace Spectre.Console.Tests.Unit
+{
+    [UsesVerify]
+    [ExpectationPath("Widgets/Columns")]
+    public sealed class ColumnsTests
+    {
+        private sealed class User
+        {
+            public string Name { get; set; }
+            public string Country { get; set; }
+        }
+
+        [Fact]
+        [Expectation("Render")]
+        public Task Should_Render_Columns_Correctly()
+        {
+            // Given
+            var console = new TestConsole().Width(61);
+            var users = new[]
+            {
+                new User { Name = "Savannah Thompson", Country = "Australia" },
+                new User { Name = "Sophie Ramos", Country = "United States" },
+                new User { Name = "Katrin Goldberg", Country = "Germany" },
+            };
+
+            var cards = new List<Panel>();
+            foreach (var user in users)
+            {
+                cards.Add(
+                    new Panel($"[b]{user.Name}[/]\n[yellow]{user.Country}[/]")
+                        .RoundedBorder().Expand());
+            }
+
+            // When
+            console.Write(new Columns(cards));
+
+            // Then
+            return Verifier.Verify(console.Output);
+        }
+    }
+}