Added Axes.stairs test in test_datetime.py (matplotlib#27424)

* Completed Axes.stairs test_datetime.py

Tested error-free

* Update test_datetime.py

* Reverting unexpected changes in test_datetime.py in the previous commit

* Update test_stairs as requested

* Fixing linting errors

* Adding Baseline data for the test

* Fixing linting error

* Update stairs test as suggested

Co-authored-by: Elliott Sales de Andrade <[email protected]>

* Update stairs test as suggested

Co-authored-by: Elliott Sales de Andrade <[email protected]>

---------

Co-authored-by: Elliott Sales de Andrade <[email protected]>

Author: ifEricReturnTrue

lib/matplotlib/tests/test_datetime.py

@@ -711,11 +711,27 @@ def test_stackplot(self):
         fig, ax = plt.subplots(layout='constrained')
         ax.stackplot(dates, stacked_nums)
 
-    @pytest.mark.xfail(reason="Test for stairs not written yet")
     @mpl.style.context("default")
     def test_stairs(self):
-        fig, ax = plt.subplots()
-        ax.stairs(...)
+        mpl.rcParams["date.converter"] = 'concise'
+
+        start_date = datetime.datetime(2023, 12, 1)
+        time_delta = datetime.timedelta(days=1)
+        baseline_date = datetime.datetime(1980, 1, 1)
+
+        bin_edges = [start_date + i * time_delta for i in range(31)]
+        edge_int = np.arange(31)
+        np.random.seed(123456)
+        values1 = np.random.randint(1, 100, 30)
+        values2 = [start_date + datetime.timedelta(days=int(i))
+                   for i in np.random.randint(1, 10000, 30)]
+        values3 = [start_date + datetime.timedelta(days=int(i))
+                   for i in np.random.randint(-10000, 10000, 30)]
+
+        fig, (ax1, ax2, ax3) = plt.subplots(3, 1, constrained_layout=True)
+        ax1.stairs(values1, edges=bin_edges)
+        ax2.stairs(values2, edges=edge_int, baseline=baseline_date)
+        ax3.stairs(values3, edges=bin_edges, baseline=baseline_date)
 
     @mpl.style.context("default")
     def test_stem(self):