TST: Split timezone preservation test into separate tests

Address review comments on PR #60080 by splitting the comprehensive test into
separate focused tests for each set operation (union, intersection, symmetric_difference).

Author: myenugula

pandas/tests/indexes/datetimes/test_setops.py

@@ -201,7 +201,7 @@ def test_union_same_timezone_different_units(self):
         expected = date_range("2000-01-01", periods=3, tz="UTC").as_unit("us")
         tm.assert_index_equal(result, expected)
 
-    def test_setops_same_nonzero_timezone_different_units(self):
+    def test_union_same_nonzero_timezone_different_units(self):
         # GH 60080 - fix timezone being changed to UTC when units differ
         # but timezone is the same
         tz = "UTC+05:00"
@@ -218,8 +218,14 @@ def test_setops_same_nonzero_timezone_different_units(self):
         tm.assert_index_equal(result, expected)
         assert result.tz == idx1.tz  # Original timezone is preserved
 
-        # Test with different dates to ensure it's not just returning one of the inputs
+    def test_union_different_dates_same_timezone_different_units(self):
+        # GH 60080 - fix timezone being changed to UTC when units differ
+        # but timezone is the same
+        tz = "UTC+05:00"
+        idx1 = date_range("2000-01-01", periods=3, tz=tz).as_unit("us")
         idx3 = date_range("2000-01-03", periods=3, tz=tz).as_unit("us")
+
+        # Test with different dates to ensure it's not just returning one of the inputs
         result = idx1.union(idx3)
         expected = DatetimeIndex(
             ["2000-01-01", "2000-01-02", "2000-01-03", "2000-01-04", "2000-01-05"],
@@ -228,14 +234,35 @@ def test_setops_same_nonzero_timezone_different_units(self):
         tm.assert_index_equal(result, expected)
         assert result.tz == idx1.tz  # Original timezone is preserved
 
+    def test_intersection_same_timezone_different_units(self):
+        # GH 60080 - fix timezone being changed to UTC when units differ
+        # but timezone is the same
+        tz = "UTC+05:00"
+        idx1 = date_range("2000-01-01", periods=3, tz=tz).as_unit("us")
+        idx2 = date_range("2000-01-01", periods=3, tz=tz).as_unit("ns")
+
+        # Check pre-conditions
+        assert idx1.tz == idx2.tz
+        assert idx1.dtype != idx2.dtype  # Different units
+
         # Test intersection
         result = idx1.intersection(idx2)
         expected = date_range("2000-01-01", periods=3, tz=tz).as_unit("ns")
         tm.assert_index_equal(result, expected)
         assert result.tz == idx1.tz  # Original timezone is preserved
 
-        # Test symmetric_difference
+    def test_symmetric_difference_same_timezone_different_units(self):
+        # GH 60080 - fix timezone being changed to UTC when units differ
+        # but timezone is the same
+        tz = "UTC+05:00"
+        idx1 = date_range("2000-01-01", periods=3, tz=tz).as_unit("us")
         idx4 = date_range("2000-01-02", periods=3, tz=tz).as_unit("ns")
+
+        # Check pre-conditions
+        assert idx1.tz == idx4.tz
+        assert idx1.dtype != idx4.dtype  # Different units
+
+        # Test symmetric_difference
         result = idx1.symmetric_difference(idx4)
         expected = DatetimeIndex(["2000-01-01", "2000-01-04"], tz=tz).as_unit("ns")
         tm.assert_index_equal(result, expected)