Add tests

BudgetApp/Services/CategoryService.cs

@@ -3,9 +3,9 @@ using BudgetApp.Data;
 
 namespace BudgetApp.Services;
 
-public class CategoryService
+public class CategoryService(ApplicationDbContext db)
 {
-    private readonly ApplicationDbContext _db;
+    private readonly ApplicationDbContext _db = db;
 
     private static readonly (string Name, string Icon)[] DefaultCategories =
     [
@@ -26,11 +26,6 @@ public class CategoryService
         ("Gifts", "🎁")
     ];
 
-    public CategoryService(ApplicationDbContext db)
-    {
-        _db = db;
-    }
-
     public async Task<List<Category>> GetCategoriesAsync(string userId)
     {
         return await _db.Categories