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<chapter id="regress">

<title id="regress-title">Regression Tests</title>

<title>Date and time differences</title>

<para>

Some of the queries in the <filename>horology</filename> test will

A few of the queries in the <filename>horology</filename> test will

fail if you run the test on the day of a daylight-saving time

changeover, or the daybefore orafter one. These queriesassume

thatthe intervals between midnight yesterday, midnight today and

changeover, or the day after one. These queriesexpect that

the intervals between midnight yesterday, midnight today and

midnight tomorrow are exactly twenty-four hours --- which is wrong

if daylight-saving time went into or out of effect meanwhile.

</para>

<note>

<para>

Because USA daylight-saving rules are used, this problem always

occurs on the first Sunday of April, the last Sunday of October,

and their following Mondays, regardless of when daylight-saving

is in effect where you live. Also note that the problem appears or

disappears at midnight Pacific time (UTC-7 or UTC-8), not midnight

your local time. Thus the failure may appear late on Saturday or

persist through much of Tuesday, depending on where you live.

</para>

</note>

<para>

Most of the date and time results are dependent on the time zone

environment. The reference files are generated for time zone