Improve error message when plotting lazy signal of ragged array

hyperspy/_signals/lazy.py

@@ -1102,6 +1102,8 @@ def post(a):
             print("\n".join([str(pr) for pr in to_print]))
 
     def plot(self, navigator='auto', **kwargs):
+        if self.axes_manager.ragged:
+            raise RuntimeError("Plotting ragged signal is not supported.")
         if isinstance(navigator, str):
             if navigator == 'spectrum':
                 # We don't support the 'spectrum' option to keep it simple

hyperspy/tests/drawing/test_plot_signal.py

@@ -333,10 +333,13 @@ def test_plot_signal_scalar():
     assert s._plot is None
 
 
-def test_plot_ragged_array():
+@pytest.mark.parametrize('lazy', [True, False])
+def test_plot_ragged_array(lazy):
     data = np.empty((2, 5), dtype=object)
     data.fill(np.array([10, 20]))
 
     s = hs.signals.BaseSignal(data, ragged=True)
+    if lazy:
+        s = s.as_lazy()
     with pytest.raises(RuntimeError):
         s.plot()