unit tests for liboffsets; fix an unraises ValueError

Author: jbrockmendel

pandas/_libs/tslibs/offsets.pyx

@@ -430,7 +430,7 @@ cpdef datetime shift_month(datetime stamp, int months, object day_opt=None):
     return stamp.replace(year=year, month=month, day=day)
 
 
-cdef int get_day_of_month(datetime other, day_opt):
+cdef int get_day_of_month(datetime other, day_opt) except? -1:
     """
     Find the day in `other`'s month that satisfies a DateOffset's onOffset
     policy, as described by the `day_opt` argument.
@@ -463,7 +463,7 @@ cdef int get_day_of_month(datetime other, day_opt):
         raise ValueError(day_opt)
 
 
-cpdef int roll_yearday(other, n, month, day_opt='start'):
+cpdef int roll_yearday(other, n, month, day_opt='start') except? -1:
     """
     Possibly increment or decrement the number of periods to shift
     based on rollforward/rollbackward conventions.

pandas/tests/tseries/offsets/test_liboffsets.py

@@ -0,0 +1,63 @@
+# -*- coding: utf-8 -*-
+"""
+Tests for helper functions in the cython tslibs.offsets
+"""
+from datetime import datetime
+
+import pytest
+
+import pandas as pd
+
+import pandas._libs.tslibs.offsets as liboffsets
+
+
+def test_shift_month():
+    dt = datetime(2017, 11, 15)
+
+    assert liboffsets.shift_month(dt, 0, day_opt=None) == dt
+    assert liboffsets.shift_month(dt, 0, day_opt=15) == dt
+
+    assert liboffsets.shift_month(dt, 1,
+                                  day_opt='start') == datetime(2017, 12, 1)
+
+    assert liboffsets.shift_month(dt, -145,
+                                  day_opt='end') == datetime(2005, 10, 31)
+
+    with pytest.raises(ValueError):
+        liboffsets.shift_month(dt, 3, day_opt='this should raise')
+
+
+def test_get_day_of_month():
+    # get_day_of_month is not directly exposed; we test it via roll_yearday
+    dt = datetime(2017, 11, 15)
+
+    with pytest.raises(ValueError):
+        # To hit the raising case we need month == dt.month and n > 0
+        liboffsets.roll_yearday(dt, n=3, month=11, day_opt='foo')
+
+
+def test_roll_yearday():
+    # Copied from doctest examples
+    month = 3
+    day_opt = 'start'              # `other` will be compared to March 1
+    other = datetime(2017, 2, 10)  # before March 1
+    assert liboffsets.roll_yearday(other, 2, month, day_opt) == 1
+    assert liboffsets.roll_yearday(other, -7, month, day_opt) == -7
+    assert liboffsets.roll_yearday(other, 0, month, day_opt) == 0
+
+    other = pd.Timestamp('2014-03-15', tz='US/Eastern')  # after March 1
+    assert liboffsets.roll_yearday(other, 2, month, day_opt) == 2
+    assert liboffsets.roll_yearday(other, -7, month, day_opt) == -6
+    assert liboffsets.roll_yearday(other, 0, month, day_opt) == 1
+
+    month = 6
+    day_opt = 'end'                # `other` will be compared to June 30
+    other = datetime(1999, 6, 29)  # before June 30
+    assert liboffsets.roll_yearday(other, 5, month, day_opt) == 4
+    assert liboffsets.roll_yearday(other, -7, month, day_opt) == -7
+    assert liboffsets.roll_yearday(other, 0, month, day_opt) == 0
+
+    other = pd.Timestamp(2072, 8, 24, 6, 17, 18)  # after June 30
+    assert liboffsets.roll_yearday(other, 5, month, day_opt) == 5
+    assert liboffsets.roll_yearday(other, -7, month, day_opt) == -6
+    assert liboffsets.roll_yearday(other, 0, month, day_opt) == 1