def METHOD_NAME(self):
    # `utc` marks a naive datetime object as being UTC, or
    # converts a timezone-aware datetime object to UTC.
    d1 = datetime.datetime(2021, 1, 1)
    d2 = datetime.datetime.strptime("2020", "%Y")
    assert d1.tzinfo is None
    assert d2.tzinfo is None
    d1_utc = to_utc(d1)
    d2_utc = to_utc(d2)
    # The wrapper function is the same as the `replace` function,
    # just less verbose.
    assert d1_utc == d1.replace(tzinfo=pytz.UTC)
    assert d2_utc == d2.replace(tzinfo=pytz.UTC)
    # The timezone information is from pytz UTC.
    assert d1_utc.tzinfo == pytz.UTC
    assert d2_utc.tzinfo == pytz.UTC
    # Passing in None gets you None.
    assert to_utc(None) == None
    # Passing in a datetime that's already UTC is a no-op.
    assert d1_utc == to_utc(d1_utc)
    # Passing in a datetime from some other timezone converts to the
    # same time in UTC.
    d1 = datetime.datetime(2021, 1, 1)
    d1_eastern = d1_utc.astimezone(pytz.timezone("US/Eastern"))
    assert d1_utc == to_utc(d1_eastern)