Open demo graph only if no files specified on command line.

test/test_mainwindow.py

@@ -26,6 +26,7 @@
 @pytest.fixture
 def app(qtbot: QtBot) -> MainWindow:
     mw = MainWindow()
+    mw.open_demo_graph()
     qtbot.addWidget(mw)
     return mw
 

zxlive/app.py

@@ -44,8 +44,11 @@ def __init__(self) -> None:
         parser.addVersionOption()
         parser.addPositionalArgument("files", "File(s) to open.", "[files...]")
         parser.process(self)
-        for f in parser.positionalArguments():
-            self.main_window.open_file_from_path(f)
+        if not parser.positionalArguments():
+            self.main_window.open_demo_graph()
+        else:
+            for f in parser.positionalArguments():
+                self.main_window.open_file_from_path(f)
 
 
 def main() -> None:

zxlive/mainwindow.py

@@ -171,6 +171,7 @@ def __init__(self) -> None:
 
         self._reset_menus(False)
 
+    def open_demo_graph(self) -> None:
         graph = construct_circuit()
         self.new_graph(graph)