TST: Adding interactive colorbar tests

Adding tests for vertical and horizontal placements, zoom in, zoom out,
and pan. Also verifying that a colorbar on a Contourset is not able
to be interacted with.

Author: greglucas

lib/matplotlib/tests/test_backend_bases.py

@@ -181,6 +181,63 @@ def test_interactive_zoom():
     assert not ax.get_autoscalex_on() and not ax.get_autoscaley_on()
 
 
+@pytest.mark.parametrize("plot_func", ["imshow", "contourf"])
+@pytest.mark.parametrize("orientation", ["vertical", "horizontal"])
+@pytest.mark.parametrize("tool,button,expected",
+                         [("zoom", MouseButton.LEFT, (4, 6)),  # zoom in
+                          ("zoom", MouseButton.RIGHT, (-20, 30)),  # zoom out
+                          ("pan", MouseButton.LEFT, (-2, 8))])
+def test_interactive_colorbar(plot_func, orientation, tool, button, expected):
+    fig, ax = plt.subplots()
+    data = np.arange(12).reshape((4, 3))
+    vmin0, vmax0 = 0, 10
+    coll = getattr(ax, plot_func)(data, vmin=vmin0, vmax=vmax0)
+
+    cb = fig.colorbar(coll, ax=ax, orientation=orientation)
+    if plot_func == "contourf":
+        # Just determine we can't navigate and exit out of the test
+        assert not cb.ax.get_navigate()
+        return
+
+    assert cb.ax.get_navigate()
+
+    # Mouse from 4 to 6 (data coordinates, "d").
+    # The y coordinate doesn't matter, just needs to be between 0 and 1
+    vmin, vmax = 4, 6
+    d0 = (vmin, 0.1)
+    d1 = (vmax, 0.9)
+    # Swap them if the orientation is vertical
+    if orientation == "vertical":
+        d0 = d0[::-1]
+        d1 = d1[::-1]
+    # Convert to screen coordinates ("s").  Events are defined only with pixel
+    # precision, so round the pixel values, and below, check against the
+    # corresponding xdata/ydata, which are close but not equal to d0/d1.
+    s0 = cb.ax.transData.transform(d0).astype(int)
+    s1 = cb.ax.transData.transform(d1).astype(int)
+
+    # Set up the mouse movements
+    start_event = MouseEvent(
+        "button_press_event", fig.canvas, *s0, button)
+    stop_event = MouseEvent(
+        "button_release_event", fig.canvas, *s1, button)
+
+    tb = NavigationToolbar2(fig.canvas)
+    if tool == "zoom":
+        tb.zoom()
+        tb.press_zoom(start_event)
+        tb.drag_zoom(stop_event)
+        tb.release_zoom(stop_event)
+    else:
+        tb.pan()
+        tb.press_pan(start_event)
+        tb.drag_pan(stop_event)
+        tb.release_pan(stop_event)
+
+    # Should be close, but won't be exact due to screen integer resolution
+    assert (cb.vmin, cb.vmax) == pytest.approx(expected, abs=0.15)
+
+
 def test_toolbar_zoompan():
     expected_warning_regex = (
         r"Treat the new Tool classes introduced in "