TST: Added test for setitem loc using datetime-like str (#45632)

Author: parthi-siva

pandas/tests/indexing/test_loc.py

@@ -2761,6 +2761,26 @@ def test_loc_setitem_uint8_upcast(value):
     tm.assert_frame_equal(df, expected)
 
 
+@pytest.mark.parametrize(
+    "fill_val,exp_dtype",
+    [
+        (Timestamp("2022-01-06"), "datetime64[ns]"),
+        (Timestamp("2022-01-07", tz="US/Eastern"), "datetime64[ns, US/Eastern]"),
+    ],
+)
+def test_loc_setitem_using_datetimelike_str_as_index(fill_val, exp_dtype):
+
+    data = ["2022-01-02", "2022-01-03", "2022-01-04", fill_val.date()]
+    index = DatetimeIndex(data, tz=fill_val.tz, dtype=exp_dtype)
+    df = DataFrame([10, 11, 12, 14], columns=["a"], index=index)
+    # adding new row using an unexisting datetime-like str index
+    df.loc["2022-01-08", "a"] = 13
+
+    data.append("2022-01-08")
+    expected_index = DatetimeIndex(data, dtype=exp_dtype)
+    tm.assert_index_equal(df.index, expected_index, exact=True)
+
+
 class TestLocSeries:
     @pytest.mark.parametrize("val,expected", [(2 ** 63 - 1, 3), (2 ** 63, 4)])
     def test_loc_uint64(self, val, expected):