add a datastar action

tests/test_web.py

@@ -134,5 +134,61 @@ def test_render_dashboard_uses_active_jobs_from_app_state() -> None:
 
         assert "27" in body
         assert "Temporary live demo counter for Datastar refresh testing" in body
+        assert "/demo/decrement" in body
+        assert "data-bind:decrement-amount" in body
+
+    asyncio.run(run())
+
+
+def test_demo_decrement_action_decrements_active_jobs() -> None:
+    async def run() -> None:
+        app = create_app(enable_demo_refresh=False)
+        broker = get_refresh_broker(app)
+        queue = broker.subscribe()
+        client = app.test_client()
+
+        response = await client.post(
+            "/demo/decrement",
+            headers={"Datastar-Request": "true"},
+            json={"decrementAmount": "3"},
+        )
+        body = await response.get_data(as_text=True)
+        event = await asyncio.wait_for(queue.get(), timeout=1)
+
+        assert response.status_code == 200
+        assert get_active_jobs(app) == 9
+        assert event == "refresh-event"
+        assert 'data: signals {"decrementError":""}' in body
+        broker.unsubscribe(queue)
+
+    asyncio.run(run())
+
+
+def test_demo_decrement_action_validates_odd_amount() -> None:
+    async def run() -> None:
+        app = create_app(enable_demo_refresh=False)
+        broker = get_refresh_broker(app)
+        queue = broker.subscribe()
+        client = app.test_client()
+
+        response = await client.post(
+            "/demo/decrement",
+            headers={"Datastar-Request": "true"},
+            json={"decrementAmount": "2"},
+        )
+        body = await response.get_data(as_text=True)
+
+        assert response.status_code == 200
+        assert get_active_jobs(app) == 12
+        assert "odd integer" in body
+
+        try:
+            await asyncio.wait_for(queue.get(), timeout=0.1)
+        except TimeoutError:
+            pass
+        else:
+            raise AssertionError("invalid decrement should not publish a refresh")
+        finally:
+            broker.unsubscribe(queue)
 
     asyncio.run(run())