add test for unit cases

Author: fgebhart

pandas/tests/tools/test_to_datetime.py

@@ -2445,7 +2445,7 @@ def test_na_to_datetime(nulls_fixture, klass):
     assert result[0] is pd.NaT
 
 
-def test_empty_string_datetime_coerce():
+def test_empty_string_datetime_coerce__format():
     # GH13044
     td = Series(["03/24/2016", "03/25/2016", ""])
     format = "%m/%d/%Y"
@@ -2462,3 +2462,15 @@ def test_empty_string_datetime_coerce():
     # don't raise an expection in case no format is given
     result = pd.to_datetime(td, errors="raise")
     pd.testing.assert_series_equal(result, expected)
+
+
+def test_empty_string_datetime_coerce__unit():
+    # GH13044
+    # coerce empty string to pd.NaT
+    result = pd.to_datetime([1, ""], unit="s", errors="coerce")
+    expected = DatetimeIndex(["1970-01-01 00:00:01", "NaT"], dtype="datetime64[ns]")
+    pd.testing.assert_index_equal(expected, result)
+
+    # verify that no exception is raised even when errors='raise' is set
+    result = pd.to_datetime([1, ""], unit="s", errors="raise")
+    pd.testing.assert_index_equal(expected, result)