Update test_broadway.py

test/demo/broadway/test_broadway.py

@@ -54,14 +54,19 @@ def on_activate(self, app):
 def test_demo(demo, browser):
     fig = get_test_figure(demo)
     app = DemoApplication(fig, application_id="io.github.slaclau.plotly_gtk.test")
+
+    def screenshot():
+        directory = (pathlib.Path(__file__).parent / "results").resolve()
+
+        browser.get("http://127.0.0.1:8085/")
+        time.sleep(5)
+        browser.save_screenshot(directory / f"{demo}.png")
+
+        img = Image.open(directory / f"{demo}.png")
+        assert np.mean(img.convert("RGB").getdata()) < 0xFF
+        app.quit()
+        return False
+    test_thread = threading.Thread(daemon=True, target=screenshot)
+    test_thread.start()
     app.run()
-
-    directory = (pathlib.Path(__file__).parent / "results").resolve()
-
-    browser.get("http://127.0.0.1:8085/")
-    time.sleep(5)
-    browser.save_screenshot(directory / f"{demo}.png")
-
-    img = Image.open(directory / f"{demo}.png")
-    assert np.mean(img.convert("RGB").getdata()) < 0xFF
-    app.quit()
+    test_thread.join()