Clean up tests

DiscordChatExporter.Cli.Tests/Utils/GlobalCache.cs

@@ -1,22 +0,0 @@
-using System;
-using System.Collections.Concurrent;
-using System.Threading.Tasks;
-
-namespace DiscordChatExporter.Cli.Tests.Utils
-{
-    internal static class GlobalCache
-    {
-        private static readonly ConcurrentDictionary<string, object?> Dictionary = new();
-
-        public static async Task<T> WrapAsync<T>(string key, Func<Task<T>> getAsync)
-        {
-            if (Dictionary.TryGetValue(key, out var value) && value is T existing)
-                return existing;
-
-            var result = await getAsync();
-            Dictionary[key] = result;
-
-            return result;
-        }
-    }
-}

DiscordChatExporter.Cli.Tests/Utils/Pollyfills.cs

@@ -0,0 +1,9 @@
+// ReSharper disable CheckNamespace
+// TODO: remove after moving to .NET 5
+
+namespace System.Runtime.CompilerServices
+{
+    internal static class IsExternalInit
+    {
+    }
+}