few corrections tests with to_datetime

Author: atbd

pandas/core/indexes/datetimes.py

@@ -332,7 +332,7 @@ def __new__(cls, data=None,
         if not (is_datetime64_dtype(data) or is_datetimetz(data) or
                 is_integer_dtype(data)):
             data = tools.to_datetime(data, dayfirst=dayfirst,
-                                     yearfirst=yearfirst)
+                                     unit='ns', yearfirst=yearfirst)
 
         if issubclass(data.dtype.type, np.datetime64) or is_datetimetz(data):
 

pandas/core/tools/datetimes.py

@@ -463,7 +463,7 @@ def check_numerical_arg():
                             .format(type(arg)))
     else:
         if (format is None and check_numerical_arg() and
-        not isinstance(arg, (DataFrame,))):
+            not isinstance(arg, (DataFrame,)) and np.asarray(arg).size):
             raise ValueError("a unit is required in case of numerical arg")
 
     # handle origin

pandas/tests/test_resample.py

@@ -1694,7 +1694,7 @@ def test_nanosecond_resample_error(self):
         start = 1443707890427
         exp_start = 1443707890400
         indx = pd.date_range(
-            start=pd.to_datetime(start),
+            start=pd.to_datetime(start, unit='ns'),
             periods=10,
             freq='100n'
         )
@@ -1703,7 +1703,7 @@ def test_nanosecond_resample_error(self):
         result = r.agg('mean')
 
         exp_indx = pd.date_range(
-            start=pd.to_datetime(exp_start),
+            start=pd.to_datetime(exp_start, unit='ns'),
             periods=10,
             freq='100n'
         )