add unit-testing framework

2020/AdventOfCode.csproj

@@ -3,6 +3,12 @@
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <TargetFramework>net5.0</TargetFramework>
+    <GenerateProgramFile>false</GenerateProgramFile>
   </PropertyGroup>
 
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.9.0" />
+    <PackageReference Include="xunit" Version="2.4.1" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.1" />
+  </ItemGroup>
 </Project>

2020/Program.cs

@@ -1,9 +1,23 @@
 using System;
+using static System.Console;
+using System.Collections.Generic;
+using Xunit;
 
 namespace AdventOfCode {
-  class Program {
+
+  public class Program {
+
+    static string Hello() {
+      return "ahoy, world";
+    }
+
+    [Fact]
+    static void HelloTest() {
+      Assert.Equal("ahoy, world", Hello());
+    }
+
     static void Main(string[] args) {
-      Console.WriteLine("Hello World!");
+      Console.WriteLine(Hello());
     }
   }
 }