Add test_step to test_datetime.py

Author: antlockyer

lib/matplotlib/tests/test_datetime.py

@@ -336,11 +336,15 @@ def test_stem(self):
         fig, ax = plt.subplots()
         ax.stem(...)
 
-    @pytest.mark.xfail(reason="Test for step not written yet")
     @mpl.style.context("default")
     def test_step(self):
-        fig, ax = plt.subplots()
-        ax.step(...)
+        mpl.rcParams["date.converter"] = "concise"
+        N = 6
+        fig, (ax1, ax2, ax3) = plt.subplots(3, 1, layout='constrained')
+        x = np.array([datetime.datetime(2023, 9, n) for n in range(1, N)])
+        ax1.step(x, range(1, N))
+        ax2.step(range(1, N), x)
+        ax3.step(x, x)
 
     @pytest.mark.xfail(reason="Test for streamplot not written yet")
     @mpl.style.context("default")