Add test_axhline in test_datetime.py

Author: CozyFrog

lib/matplotlib/tests/test_datetime.py

@@ -26,12 +26,18 @@ def test_arrow(self):
         fig, ax = plt.subplots()
         ax.arrow(...)
 
-    @pytest.mark.xfail(reason="Test for axhline not written yet")
     @mpl.style.context("default")
     def test_axhline(self):
         mpl.rcParams["date.converter"] = 'concise'
-        fig, ax = plt.subplots(layout='constrained')
-        ax.axhline(y=datetime.datetime(2020, 6, 1), xmin=0.2, xmax=0.8)
+        fig, (ax1, ax2, ax3) = plt.subplots(3, 1, layout='constrained')
+        ax1.set_ylim(bottom=datetime.datetime(2020, 4, 1),
+                     top=datetime.datetime(2020, 8, 1))
+        ax2.set_ylim(bottom=np.datetime64('2005-01-01'),
+                     top=np.datetime64('2005-04-01'))
+        ax3.set_ylim(bottom=datetime.datetime(2023, 9, 1),
+                     top=datetime.datetime(2023, 11, 1))
+        ax1.axhline(y=datetime.datetime(2020, 6, 3), xmin=0.5, xmax=0.7)
+        ax2.axhline(np.datetime64('2005-02-25T03:30'), xmin=0.1, xmax=0.9)
 
     @pytest.mark.xfail(reason="Test for axhspan not written yet")
     @mpl.style.context("default")