Re: Timezone error when casting. Maybe daylight saving

Kjetil =?ISO-8859-1?Q?Nyg=E5rd?= <polpot78(at)gmail(dot)com> writes:
> I try to build with the tests, but when I run the test
> org.postgresql.test.jdbc2.StatementTest.testDateFunctions() i get:
> junit.framework.AssertionFailedError: expected:<-3> but was:<-2>

> When I run the same function directly in PostgreSQL, I also get -2:

> test=> select extract( day from ((CAST(-3 || ' day' as
> interval)+now())-now()));
> date_part
> -----------
> -2

I get -3 ... unless I set my timezone to Europe/Oslo. I'm guessing
that you had a daylight savings transition this past weekend? If so,
the issue is that the query gives a different answer for a couple
of days after a transition, as a consequence of the fact that adding
'1 day' to a timestamp is not the same as adding '24 hours'.

We used to have issues of this sort with the core regression tests;
they'd fail predictably for a couple of days in spring and fall.
Eventually we changed all the test cases to not hit the boundary
condition ... which is arguably a loss of test coverage, but it
wasn't worth the hassle of having unstable regression test results.
It sounds like JDBC's test cases still have the issue.

regards, tom lane