Add way to get clear checkpoints for starting new time periods

pytest.ini

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+[pytest]
+norecursedirs = ve
+addopts=--tb=short

teamanalysis/time.py

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+import calendar
+import datetime
+
+def get_checkpoint(n):
+    day_of_week = n.isoweekday()
+    new_day = n - datetime.timedelta(days=(day_of_week-1))
+    checkpoint = datetime.datetime(new_day.year, new_day.month, new_day.day, 0, 0, 0, 1)
+    return checkpoint

tests/test_time.py

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+import datetime
+import pytest
+import teamanalysis.time
+
+@pytest.mark.parametrize('when, expected', [
+    (datetime.datetime(2015, 7, 30, 20, 35, 35, 784435), datetime.datetime(2015, 7, 27, 0, 0, 0, 1)),
+    (datetime.datetime(2015, 1, 3, 2, 5, 5, 7835), datetime.datetime(2014, 12, 29, 0, 0, 0, 1)),
+    (datetime.datetime(2015, 1, 5, 2, 5, 5, 7835), datetime.datetime(2015, 1, 5, 0, 0, 0, 1)),
+])
+def test_checkpoint(when, expected):
+    checkpoint = teamanalysis.time.get_checkpoint(when)
+    assert checkpoint == expected
+