Add test for no pending migrations

src/tests/test_no_missing_migrations.py

@@ -0,0 +1,18 @@
+from io import StringIO
+
+import pytest
+from django.core.management import call_command
+
+
+@pytest.mark.django_db
+def test_no_pending_migrations():
+    out = StringIO()
+    try:
+        call_command(
+            "makemigrations",
+            "--check",
+            stdout=out,
+            stderr=StringIO(),
+        )
+    except SystemExit:  # pragma: no cover
+        raise AssertionError("Pending migrations:\n" + out.getvalue()) from None