Refactor the chrono cast functions into chrono.h.

Add unit tests and documentation for the chrono cast.

tests/test_chrono.py

@@ -0,0 +1,102 @@
+
+
+def test_chrono_system_clock():
+    from pybind11_tests import test_chrono1
+    import datetime
+
+    # Get the time from both c++ and datetime
+    date1 = test_chrono1()
+    date2 = datetime.datetime.today()
+
+    # The returned value should be a datetime
+    assert isinstance(date1, datetime.datetime)
+
+    # The numbers should vary by a very small amount (time it took to execute)
+    diff = abs(date1 - date2)
+
+    # There should never be a days/seconds difference
+    assert diff.days == 0
+    assert diff.seconds == 0
+
+    # 500 microseconds is a very long time to execute this
+    assert diff.microseconds < 500
+
+
+def test_chrono_system_clock_roundtrip():
+    from pybind11_tests import test_chrono2
+    import datetime
+
+    date1 = datetime.datetime.today()
+
+    # Roundtrip the time
+    date2 = test_chrono2(date1)
+
+    # The returned value should be a datetime
+    assert isinstance(date2, datetime.datetime)
+
+    # They should be identical (no information lost on roundtrip)
+    diff = abs(date1 - date2)
+    assert diff.days == 0
+    assert diff.seconds == 0
+    assert diff.microseconds == 0
+
+
+def test_chrono_duration_roundtrip():
+    from pybind11_tests import test_chrono3
+    import datetime
+
+    # Get the difference betwen two times (a timedelta)
+    date1 = datetime.datetime.today()
+    date2 = datetime.datetime.today()
+    diff = date2 - date1
+
+    # Make sure this is a timedelta
+    assert isinstance(diff, datetime.timedelta)
+
+    cpp_diff = test_chrono3(diff)
+
+    assert cpp_diff.days == diff.days
+    assert cpp_diff.seconds == diff.seconds
+    assert cpp_diff.microseconds == diff.microseconds
+
+
+def test_chrono_duration_subtraction_equivalence():
+    from pybind11_tests import test_chrono4
+    import datetime
+
+    date1 = datetime.datetime.today()
+    date2 = datetime.datetime.today()
+
+    diff = date2 - date1
+    cpp_diff = test_chrono4(date2, date1)
+
+    assert cpp_diff.days == diff.days
+    assert cpp_diff.seconds == diff.seconds
+    assert cpp_diff.microseconds == diff.microseconds
+
+
+def test_chrono_steady_clock():
+    from pybind11_tests import test_chrono5
+    import datetime
+
+    time1 = test_chrono5()
+    time2 = test_chrono5()
+
+    assert isinstance(time1, datetime.time)
+    assert isinstance(time2, datetime.time)
+
+
+def test_chrono_steady_clock_roundtrip():
+    from pybind11_tests import test_chrono6
+    import datetime
+
+    time1 = datetime.time(second=10, microsecond=100)
+    time2 = test_chrono6(time1)
+
+    assert isinstance(time2, datetime.time)
+
+    # They should be identical (no information lost on roundtrip)
+    assert time1.hour == time2.hour
+    assert time1.minute == time2.minute
+    assert time1.second == time2.second
+    assert time1.microsecond == time2.microsecond