Improve robustness in Dates/conversions test (#49086)
* Improve robustness in Dates/conversions test
In [1], this test was observed to fail, with a 1 second pause between
the two Dates.now calls. In general, particularly on high-load CI
systems, we cannot make assumptions that calls will complete within
any particular amount of time. Instead, we should be asserting
properties that should be universally true. This test wants to
assert that Dates.now() and Dates.now(UTC) give the same answer
if the TZ environment variable is set appropriately, but of course
we can't guarantee that these calls run at the same time. Rather
than setting an arbitrary limit of 1 second, just run `Dates.now`
again. Our semantics guarantee ordering of these calls (in the
absence of leap days/seconds at least), so the test is more robust.
[1] https://buildkite.com/julialang/julia-master/builds/22064#0186ff11-f07e-4ba4-9b54-21bdf738d35e
* now: Consistently truncate DateTime rather than rounding
The operating system clock provides the current time in microseconds,
but `DateTime` has milisecond precision. The question is what rounding
to apply. `now` was using truncation, while `now(UTC)` was using rounding.
I think truncation is probably the better default, since you're often
interested in whether a particular `DateTime` has passed, so change `now(UTC)`
to trucate as well.
