directory for a VPATH build in a similar
    way to how it is done for the core code. One way to do this is using the
    core script <filename>config/prep_buildtree</filename>. Once this has been done
    you can build by setting the <literal>make</literal> variable
    <varname>VPATH</varname> like this:
<programlisting>
make VPATH=/path/to/extension/source/tree
make VPATH=/path/to/extension/source/tree install
</programlisting>
    This procedure can work with a greater variety of directory layouts.
   </para>

   <para>
    The scripts listed in the <varname>REGRESS</varname> variable are used for
    regression testing of your module, which can be invoked by <literal>make
    installcheck</literal> after doing <literal>make install</literal>.  For this to
    work you must have a running <productname>PostgreSQL</productname> server.
    The script files listed in <varname>REGRESS</varname> must appear in a
    subdirectory named <literal>sql/</literal> in your extension's directory.
    These files must have extension <literal>.sql</literal>, which must not be
    included in the <varname>REGRESS</varname> list in the makefile.  For each
    test there should also be a file containing the expected output in a
    subdirectory named <literal>expected/</literal>, with the same stem and
    extension <literal>.out</literal>.  <literal>make installcheck</literal>
    executes each test script with <application>psql</application>, and compares the
    resulting output to the matching expected file.  Any differences will be
    written to the file <literal>regression.diffs</literal> in <command>diff
    -c</command> format.  Note that trying to run a test that is missing its
    expected file will be reported as <quote>trouble</quote>, so make sure you
    have all expected files.
   </para>

   <para>
    The scripts listed in the <varname>ISOLATION</varname> variable are used
    for tests stressing behavior of concurrent session with your module, which
    can be invoked by <literal>make installcheck</literal> after doing
    <literal>make install</literal>.  For this to work you must have a
    running <productname>PostgreSQL</productname> server.  The script files
    listed in <varname>ISOLATION</varname> must appear in a subdirectory
    named <literal>specs/</literal> in your extension's directory.  These files
    must have extension <literal>.spec</literal>, which must not be included
    in the <varname>ISOLATION</varname> list in the makefile.  For each test
    there should also be a file containing the expected output in a
    subdirectory named <literal>expected/</literal>, with the same stem and
    extension <literal>.out</literal>.  <literal>make installcheck</literal>
    executes each test script, and compares the resulting output to the
    matching expected file.  Any differences will be written to the file
    <literal>output_iso/regression.diffs</literal> in
    <command>diff -c</command> format.  Note that trying to run a test that is
    missing its expected file will be reported as <quote>trouble</quote>, so
    make sure you have all expected files.
   </para>

   <para>
    <literal>TAP_TESTS</literal> enables the use of TAP tests.  Data from each
    run is present in a subdirectory named <literal>tmp_check/</literal>.
    See also <xref linkend="regress-tap"/> for more details.
   </para>

   <tip>
    <para>
     The easiest way to create the expected files is to create empty files,
     then do a test run (which will of course report differences).  Inspect
     the actual result files found in the <literal>results/</literal>
     directory (for tests in <literal>REGRESS</literal>), or
     <literal>output_iso/results/</literal> directory (for tests in
     <literal>ISOLATION</literal>), then copy them to
     <literal>expected/</literal> if they match what you expect from the test.
    </para>

   </tip>
  </sect1>

 </chapter>