Add test_contour under test_datetime.py (matplotlib#27013)

* Add test_contour matplotlib#26864

* Add test_contour matplotlib#26864

Modify test_contour matplotlib#26864

* Removed test_cohere and repetitive tests

Author: kots14

lib/matplotlib/tests/test_datetime.py

@@ -265,11 +265,29 @@ def test_clabel(self):
         fig, ax = plt.subplots()
         ax.clabel(...)
 
-    @pytest.mark.xfail(reason="Test for contour not written yet")
     @mpl.style.context("default")
     def test_contour(self):
-        fig, ax = plt.subplots()
-        ax.contour(...)
+        mpl.rcParams["date.converter"] = "concise"
+        range_threshold = 10
+        fig, (ax1, ax2, ax3) = plt.subplots(3, 1, layout="constrained")
+
+        x_dates = np.array(
+            [datetime.datetime(2023, 10, delta) for delta in range(1, range_threshold)]
+        )
+        y_dates = np.array(
+            [datetime.datetime(2023, 10, delta) for delta in range(1, range_threshold)]
+        )
+        x_ranges = np.array(range(1, range_threshold))
+        y_ranges = np.array(range(1, range_threshold))
+
+        X_dates, Y_dates = np.meshgrid(x_dates, y_dates)
+        X_ranges, Y_ranges = np.meshgrid(x_ranges, y_ranges)
+
+        Z_ranges = np.cos(X_ranges / 4) + np.sin(Y_ranges / 4)
+
+        ax1.contour(X_dates, Y_dates, Z_ranges)
+        ax2.contour(X_dates, Y_ranges, Z_ranges)
+        ax3.contour(X_ranges, Y_dates, Z_ranges)
 
     @mpl.style.context("default")
     def test_contourf(self):