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>Chapter 26. Regression Tests</TD
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CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="REGRESS-EVALUATION"
>26.2. Test Evaluation</A
></H1
><P
> Some properly installed and fully functional
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> installations can
<SPAN
CLASS="QUOTE"
>"fail"</SPAN
> some of these regression tests due to
platform-specific artifacts such as varying floating-point representation
and time zone support. The tests are currently evaluated using a simple
<TT
CLASS="COMMAND"
>diff</TT
> comparison against the outputs
generated on a reference system, so the results are sensitive to
small system differences. When a test is reported as
<SPAN
CLASS="QUOTE"
>"failed"</SPAN
>, always examine the differences between
expected and actual results; you may well find that the
differences are not significant. Nonetheless, we still strive to
maintain accurate reference files across all supported platforms,
so it can be expected that all tests pass.
</P
><P
> The actual outputs of the regression tests are in files in the
<TT
CLASS="FILENAME"
>src/test/regress/results</TT
> directory. The test
script uses <TT
CLASS="COMMAND"
>diff</TT
> to compare each output
file against the reference outputs stored in the
<TT
CLASS="FILENAME"
>src/test/regress/expected</TT
> directory. Any
differences are saved for your inspection in
<TT
CLASS="FILENAME"
>src/test/regress/regression.diffs</TT
>. (Or you
can run <TT
CLASS="COMMAND"
>diff</TT
> yourself, if you prefer.)
</P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN22417"
>26.2.1. Error message differences</A
></H2
><P
> Some of the regression tests involve intentional invalid input
values. Error messages can come from either the
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> code or from the host
platform system routines. In the latter case, the messages may
vary between platforms, but should reflect similar
information. These differences in messages will result in a
<SPAN
CLASS="QUOTE"
>"failed"</SPAN
> regression test that can be validated by
inspection.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN22422"
>26.2.2. Locale differences</A
></H2
><P
> If you run the tests against an already-installed server that was
initialized with a collation-order locale other than C, then
there may be differences due to sort order and follow-up
failures. The regression test suite is set up to handle this
problem by providing alternative result files that together are
known to handle a large number of locales. For example, for the
<TT
CLASS="LITERAL"
>char</TT
> test, the expected file
<TT
CLASS="FILENAME"
>char.out</TT
> handles the <TT
CLASS="LITERAL"
>C</TT
> and <TT
CLASS="LITERAL"
>POSIX</TT
> locales,
and the file <TT
CLASS="FILENAME"
>char_1.out</TT
> handles many other
locales. The regression test driver will automatically pick the
best file to match against when checking for success and for
computing failure differences. (This means that the regression
tests cannot detect whether the results are appropriate for the
configured locale. The tests will simply pick the one result
file that works best.)
</P
><P
> If for some reason the existing expected files do not cover some
locale, you can add a new file. The naming scheme is
<TT
CLASS="LITERAL"
><TT
CLASS="REPLACEABLE"
><I
>testname</I
></TT
>_<TT
CLASS="REPLACEABLE"
><I
>digit</I
></TT
>.out</TT
>.
The actual digit is not significant. Remember that the
regression test driver will consider all such files to be equally
valid test results. If the test results are platform-specific,
the technique described in <A
HREF="regress-platform.html"
>Section 26.3</A
>
should be used instead.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN22435"
>26.2.3. Date and time differences</A
></H2
><P
> A few of the queries in the <TT
CLASS="FILENAME"
>horology</TT
> test will
fail if you run the test on the day of a daylight-saving time
changeover, or the day after one. These queries expect 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.
</P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
> Because USA daylight-saving time 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 time
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.
</P
></BLOCKQUOTE
></DIV
><P
> Most of the date and time results are dependent on the time zone
environment. The reference files are generated for time zone
<TT
CLASS="LITERAL"
>PST8PDT</TT
> (Berkeley, California), and there will be
apparent failures if the tests are not run with that time zone setting.
The regression test driver sets environment variable
<TT
CLASS="ENVAR"
>PGTZ</TT
> to <TT
CLASS="LITERAL"
>PST8PDT</TT
>, which normally
ensures proper results.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN22445"
>26.2.4. Floating-point differences</A
></H2
><P
> Some of the tests involve computing 64-bit floating-point numbers (<TT
CLASS="TYPE"
>double
precision</TT
>) from table columns. Differences in
results involving mathematical functions of <TT
CLASS="TYPE"
>double
precision</TT
> columns have been observed. The <TT
CLASS="LITERAL"
>float8</TT
> and
<TT
CLASS="LITERAL"
>geometry</TT
> tests are particularly prone to small differences
across platforms, or even with different compiler optimization options.
Human eyeball comparison is needed to determine the real
significance of these differences which are usually 10 places to
the right of the decimal point.
</P
><P
> Some systems display minus zero as <TT
CLASS="LITERAL"
>-0</TT
>, while others
just show <TT
CLASS="LITERAL"
>0</TT
>.
</P
><P
> Some systems signal errors from <CODE
CLASS="FUNCTION"
>pow()</CODE
> and
<CODE
CLASS="FUNCTION"
>exp()</CODE
> differently from the mechanism
expected by the current <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>
code.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN22459"
>26.2.5. Row ordering differences</A
></H2
><P
>You might see differences in which the same rows are output in a
different order than what appears in the expected file. In most cases
this is not, strictly speaking, a bug. Most of the regression test
scripts are not so pedantic as to use an <TT
CLASS="LITERAL"
>ORDER BY</TT
> for every single
<TT
CLASS="LITERAL"
>SELECT</TT
>, and so their result row orderings are not well-defined
according to the letter of the SQL specification. In practice, since we are
looking at the same queries being executed on the same data by the same
software, we usually get the same result ordering on all platforms, and
so the lack of <TT
CLASS="LITERAL"
>ORDER BY</TT
> isn't a problem. Some queries do exhibit
cross-platform ordering differences, however. (Ordering differences
can also be triggered by non-C locale settings.)
</P
><P
>Therefore, if you see an ordering difference, it's not something to
worry about, unless the query does have an <TT
CLASS="LITERAL"
>ORDER BY</TT
> that your result
is violating. But please report it anyway, so that we can add an
<TT
CLASS="LITERAL"
>ORDER BY</TT
> to that particular query and thereby eliminate the bogus
<SPAN
CLASS="QUOTE"
>"failure"</SPAN
> in future releases.
</P
><P
>You might wonder why we don't order all the regression test queries explicitly to
get rid of this issue once and for all. The reason is that that would
make the regression tests less useful, not more, since they'd tend
to exercise query plan types that produce ordered results to the
exclusion of those that don't.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN22470"
>26.2.6. The <SPAN
CLASS="QUOTE"
>"random"</SPAN
> test</A
></H2
><P
> The <TT
CLASS="LITERAL"
>random</TT
> test script is intended to produce
random results. In rare cases, this causes the random regression
test to fail. Typing
</P><PRE
CLASS="PROGRAMLISTING"
>diff results/random.out expected/random.out</PRE
><P>
should produce only one or a few lines of differences. You need
not worry unless the random test fails repeatedly.
</P
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