add some tests and generate images

Author: ZHANGROU-99

nbs/tests/baseline_images/test_71_unpaired_delta_g.png

@@ -152,4 +152,16 @@ def test_58_delta_axes_invert_ylim():
 def test_59_delta_axes_invert_ylim_not_showing_delta2():
     return unpaired.mean_diff.plot(delta2_ylim=(2, -2),
                                    delta2_label="More negative is better!",
-                                   show_delta2=False);
+                                   show_delta2=False);
+
+@pytest.mark.mpl_image_compare(tolerance=10)
+def test_71_unpaired_delta_g():
+    return unpaired.delta_g.plot();
+
+@pytest.mark.mpl_image_compare(tolerance=10)
+def test_72_sequential_delta_g():
+    return sequential.mean_diff.plot();
+
+@pytest.mark.mpl_image_compare(tolerance=10)
+def test_73_baseline_delta_g():
+    return baseline.mean_diff.plot();