TST: Test searchsorted for monotonic decreasing index (#58692)

pandas/tests/indexes/test_common.py

@@ -270,9 +270,7 @@ def test_searchsorted_monotonic(self, index_flat, request):
             # all values are the same, expected_right should be length
             expected_right = len(index)
 
-        # test _searchsorted_monotonic in all cases
-        # test searchsorted only for increasing
-        if index.is_monotonic_increasing:
+        if index.is_monotonic_increasing or index.is_monotonic_decreasing:
             ssm_left = index._searchsorted_monotonic(value, side="left")
             assert expected_left == ssm_left
 
@@ -284,13 +282,6 @@ def test_searchsorted_monotonic(self, index_flat, request):
 
             ss_right = index.searchsorted(value, side="right")
             assert expected_right == ss_right
-
-        elif index.is_monotonic_decreasing:
-            ssm_left = index._searchsorted_monotonic(value, side="left")
-            assert expected_left == ssm_left
-
-            ssm_right = index._searchsorted_monotonic(value, side="right")
-            assert expected_right == ssm_right
         else:
             # non-monotonic should raise.
             msg = "index must be monotonic increasing or decreasing"