Add tests

BudgetApp/Services/TransactionService.cs

@@ -3,14 +3,9 @@ using BudgetApp.Data;
 
 namespace BudgetApp.Services;
 
-public class TransactionService
+public class TransactionService(ApplicationDbContext db)
 {
-    private readonly ApplicationDbContext _db;
-
-    public TransactionService(ApplicationDbContext db)
-    {
-        _db = db;
-    }
+    private readonly ApplicationDbContext _db = db;
 
     public async Task<List<Transaction>> GetTransactionsAsync(string userId)
     {
@@ -248,7 +243,7 @@ public class TransactionService
         }
     }
 
-    private static DateTime GetNextOccurrence(DateTime current, RecurrenceType recurrence) => recurrence switch
+    internal static DateTime GetNextOccurrence(DateTime current, RecurrenceType recurrence) => recurrence switch
     {
         RecurrenceType.Daily => current.AddDays(1),
         RecurrenceType.Weekly => current.AddDays(7),