feat: improve admin and add demo data command

backend/shows/test_management.py

@@ -0,0 +1,31 @@
+from django.core.management import call_command
+from django.test import TestCase
+
+from shows.models import Performance, Show, Venue
+
+
+class SeedDemoDataCommandTests(TestCase):
+    def test_seed_demo_data_runs_successfully(self):
+        call_command("seed_demo_data")
+
+        self.assertEqual(Show.objects.count(), 2)
+        self.assertEqual(Venue.objects.count(), 2)
+        self.assertEqual(Performance.objects.count(), 3)
+        self.assertTrue(Show.objects.filter(is_published=True).exists())
+
+    def test_seed_demo_data_is_idempotent(self):
+        call_command("seed_demo_data")
+        first_counts = (
+            Show.objects.count(),
+            Venue.objects.count(),
+            Performance.objects.count(),
+        )
+
+        call_command("seed_demo_data")
+        second_counts = (
+            Show.objects.count(),
+            Venue.objects.count(),
+            Performance.objects.count(),
+        )
+
+        self.assertEqual(first_counts, second_counts)