Use one figure per test, not the global one. Save the resulting plot.

ctapipe/visualization/tests/test_mpl.py

@@ -64,8 +64,9 @@ def test_camera_display_single(prod5_lst_cam, tmp_path):
     """test CameraDisplay functionality"""
     from ..mpl_camera import CameraDisplay
 
+    fig, ax = plt.subplots()
     geom = prod5_lst_cam
-    disp = CameraDisplay(geom)
+    disp = CameraDisplay(geom, ax=ax)
     image = np.random.normal(size=len(geom.pix_x))
     disp.image = image
     disp.add_colorbar()
@@ -86,36 +87,41 @@ def test_camera_display_single(prod5_lst_cam, tmp_path):
 
     disp.add_ellipse(centroid=(0, 0), width=0.1, length=0.1, angle=0.1)
     disp.clear_overlays()
+    fig.savefig(tmp_path / "result.png")
 
 
-def test_hillas_overlay(prod5_lst_cam):
+def test_hillas_overlay(prod5_lst_cam, tmp_path):
     from ctapipe.visualization import CameraDisplay
 
-    disp = CameraDisplay(prod5_lst_cam)
+    fig, ax = plt.subplots()
+    disp = CameraDisplay(prod5_lst_cam, ax=ax)
     hillas = CameraHillasParametersContainer(
         x=0.1 * u.m, y=-0.1 * u.m, length=0.5 * u.m, width=0.2 * u.m, psi=90 * u.deg
     )
 
-    disp.overlay_moments(hillas)
+    disp.overlay_moments(hillas, color="w")
+    fig.savefig(tmp_path / "result.png")
 
 
 @pytest.mark.parametrize("pix_type", PixelShape.__members__.values())
-def test_pixel_shapes(pix_type, prod5_lst_cam):
+def test_pixel_shapes(pix_type, prod5_lst_cam, tmp_path):
     """test CameraDisplay functionality"""
     from ..mpl_camera import CameraDisplay
 
     geom = prod5_lst_cam
     geom.pix_type = pix_type
 
-    disp = CameraDisplay(geom)
+    fig, ax = plt.subplots()
+    disp = CameraDisplay(geom, ax=ax)
     image = np.random.normal(size=len(geom.pix_x))
     disp.image = image
     disp.add_colorbar()
     disp.highlight_pixels([1, 2, 3, 4, 5])
     disp.add_ellipse(centroid=(0, 0), width=0.1, length=0.1, angle=0.1)
+    fig.savefig(tmp_path / "result.png")
 
 
-def test_camera_display_multiple(prod5_lst_cam):
+def test_camera_display_multiple(prod5_lst_cam, tmp_path):
     """create a figure with 2 subplots, each with a CameraDisplay"""
     from ..mpl_camera import CameraDisplay
 
@@ -128,6 +134,7 @@ def test_camera_display_multiple(prod5_lst_cam):
     image = np.ones(len(geom.pix_x), dtype=float)
     d1.image = image
     d2.image = image
+    fig.savefig(tmp_path / "result.png")
 
 
 def test_array_display(prod5_mst_nectarcam):