Basic implementation of invoice call validation

counter/tests/test_invoices.py

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+from datetime import date
+
+import pytest
+from model_bakery import baker
+
+from club.models import Club
+from counter.models import InvoiceCall
+
+
+@pytest.mark.django_db
+def test_invoice_date_with_date():
+    club = baker.make(Club)
+    invoice = InvoiceCall.objects.create(club=club, month=date(2025, 10, 20))
+
+    assert not invoice.is_validated
+    assert str(invoice) == f"invoice call of {invoice.month} made by {club}"
+    assert invoice.month == date(2025, 10, 1)
+
+
+@pytest.mark.django_db
+def test_invoice_date_with_string():
+    club = baker.make(Club)
+    invoice = InvoiceCall.objects.create(club=club, month="2025-10")
+
+    assert invoice.month == date(2025, 10, 1)
+
+
+@pytest.mark.django_db
+def test_invoice_call_invalid_month_string():
+    club = baker.make(Club)
+
+    with pytest.raises(ValueError):
+        InvoiceCall.objects.create(club=club, month="2025-13")