Working on the UserRepository functionality

+ Tests
+ QueryableExtensions. It is an add-on that allows you to implement exceptions if the returned List would be empty.

Govor.Core/Infrastructure/Extensions/QueryableExtensions.cs

@@ -0,0 +1,13 @@
+using Microsoft.EntityFrameworkCore;
+
+namespace Govor.Core.Infrastructure.Extensions;
+
+public static class QueryableExtensions
+{
+    public static async Task<List<T>> ToListOrThrowIfEmpty<T>(this IQueryable<T> query, Exception ex)
+    {
+        var list = await query.ToListAsync();
+        if (list.Count == 0) throw ex;
+        return list;
+    }
+}