DOC: fix parameters line in Axes.axis docstring

Author: phobson

lib/matplotlib/axes/_base.py

@@ -1628,7 +1628,7 @@ def axis(self, *args, **kwargs):
 
         Parameters
         ----------
-        xmin, ymin, xmax, ymax : float, optional
+        xmin, xmax, ymin, ymax : float, optional
             The axis limits to be set. Either none or all of the limits must
             be given. This can also be achieved using ::
 

lib/matplotlib/tests/test_axes.py

@@ -6450,6 +6450,22 @@ def test_axis_bool_arguments(fig_test, fig_ref):
     fig_ref.add_subplot(212).axis("on")
 
 
+def test_axis_extent_arg():
+    fig, ax = plt.subplots()
+    xmin = 5
+    xmax = 10
+    ymin = 15
+    ymax = 20
+    extent = ax.axis([xmin, xmax, ymin, ymax])
+
+    # test that the docstring is correct
+    assert tuple(extent) == (xmin, xmax, ymin, ymax)
+
+    # test that limits were set per the docstring
+    assert (xmin, xmax) == ax.get_xlim()
+    assert (ymin, ymax) == ax.get_ylim()
+
+
 def test_datetime_masked():
     # make sure that all-masked data falls back to the viewlim
     # set in convert.axisinfo....