Fix offset error when subtracting datetimes in the same tz

Author: sdispater

CHANGELOG.md

@@ -1,5 +1,12 @@
 # Change Log
 
+## [Unreleased]
+
+### Fixed
+
+- Fixed an offset error when subtracting datetimes in the same timezone.
+
+
 ## [1.4.1] - 2018-02-05
 
 ### Fixed

pendulum/helpers.py

@@ -194,7 +194,10 @@ def precise_diff(d1, d2):
     if hasattr(d2, 'hour'):
         # If we are not in the same timezone
         # we need to adjust
-        if not in_same_tz:
+        #
+        # We also need to adjust if we do not
+        # have variable-length units
+        if not in_same_tz or total_days == 0:
             offset1 = d1.utcoffset()
             offset2 = d2.utcoffset()
 

tests/period_tests/test_add_subtract.py

@@ -12,6 +12,15 @@ def test_dst_add():
     assert new_end == end
 
 
+def test_dst_add_non_variable_units():
+    start = pendulum.create(2013, 3, 31, 1, 30, tz='Europe/Paris')
+    end = start.add(hours=1)
+    period = end - start
+    new_end = start + period
+
+    assert new_end == end
+
+
 def test_dst_subtract():
     start = pendulum.create(2017, 3, 7, tz='America/Toronto')
     end = start.add(days=6)