<!-- doc/src/sgml/regress.sgml -->

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

  <indexterm zone="regress">
   <primary>regression tests</primary>
  </indexterm>

  <indexterm zone="regress">
   <primary>test</primary>
  </indexterm>

  <para>
   The regression tests are a comprehensive set of tests for the SQL
   implementation in <productname>PostgreSQL</productname>.  They test
   standard SQL operations as well as the extended capabilities of
   <productname>PostgreSQL</productname>.
  </para>

  <sect1 id="regress-run">
   <title>Running the Tests</title>

  <para>
   The regression tests can be run against an already installed and
   running server, or using a temporary installation within the build
   tree.  Furthermore, there is a <quote>parallel</quote> and a
   <quote>sequential</quote> mode for running the tests.  The
   sequential method runs each test script alone, while the
   parallel method starts up multiple server processes to run groups
   of tests in parallel.  Parallel testing adds confidence that
   interprocess communication and locking are working correctly.
  </para>

  <sect2>
   <title>Running the Tests Against a Temporary Installation</title>

  <para>
   To run the parallel regression tests after building but before installation,
   type:
<screen>
make check
</screen>
   in the top-level directory.  (Or you can change to
   <filename>src/test/regress</filename> and run the command there.)
   At the end you should see something like:
<screen>
<computeroutput>
=======================
 All 115 tests passed.
=======================
</computeroutput>
</screen>
   or otherwise a note about which tests failed.  See <xref
   linkend="regress-evaluation"/> below before assuming that a
   <quote>failure</quote> represents a serious problem.
  </para>

   <para>
    Because this test method runs a temporary server, it will not work
    if you did the build as the root user, since the server will not start as
    root.  Recommended procedure is not to do the build as root, or else to
    perform testing after completing the installation.
   </para>

   <para>
    If you have configured <productname>PostgreSQL</productname> to install
    into a location where an older <productname>PostgreSQL</productname>
    installation already exists, and you perform <literal>make check</literal>
    before installing the new version, you might find that the tests fail
    because the new programs try to use the already-installed shared
    libraries.  (Typical symptoms are complaints about undefined symbols.)
    If you wish to run the tests before overwriting the old installation,
    you'll need to build with <literal>configure --disable-rpath</literal>.
    It is not recommended that you use this option for the final installation,
    however.
   </para>

   <para>
    The parallel regression test starts quite a few processes under your
    user ID.  Presently, the maximum concurrency is twenty parallel test
    scripts, which means forty processes: there's a server process and a
    <application>psql</application> process for each test script.
    So if your system enforces a per-user limit on the number of processes,
    make sure this limit is at least fifty or so, else you might get
    random-seeming failures in the parallel test.  If you are not in
    a position to raise the limit, you can cut down the degree of parallelism
    by setting the <literal>MAX_CONNECTIONS</literal> parameter.  For example:
<screen>
make MAX_CONNECTIONS=10 check
</screen>
    runs no more than ten tests concurrently.
   </para>
  </sect2>

  <sect2>
   <title>Running the Tests Against an Existing Installation</title>

  <para>
   To run the tests after installation (see <xref linkend="installation"/>),
   initialize a data area and start the
   server as explained in <xref linkend="runtime"/>, then type:
<screen>
make installcheck
</screen>
or for a parallel test:
<screen>
make installcheck-parallel
</screen>
   The tests will expect to contact the server at the local host and the
   default port number, unless directed otherwise by <envar>PGHOST</envar> and
   <envar>PGPORT</envar> environment variables.  The tests will be run in a
   database named <literal>regression</literal>; any existing database by this name
   will be dropped.
  </para>

  <para>
   The tests will also transiently create some cluster-wide objects, such as
   roles and tablespaces.  These objects will have names beginning with
   <literal>regress_</literal>.  Beware of using <literal>installcheck</literal>
   mode in installations that have any actual users or tablespaces named
   that way.
  </para>
  </sect2>

  <sect2>
   <title>Additional Test Suites</title>

  <para>
   The <literal>make check</literal> and <literal>make installcheck</literal> commands
   run only the <quote>core</quote> regression tests, which test built-in
   functionality of the <productname>PostgreSQL</productname> server.  The source
   distribution also contains additional test suites, most of them having
   to do with add-on functionality such as optional procedural languages.
  </para>

  <para>
   To run all test suites applicable to the modules that have been selected
   to be built, including the core tests, type one of these commands at the
   top of the build tree:
<screen>
make check-world
make installcheck-world
</screen>
   These commands run the tests using temporary servers or an
   already-installed server, respectively, just as previously explained
   for <literal>make check</literal> and <literal>make installcheck</literal>.  Other
   considerations are the same as previously explained for each method.
   Note that <literal>make check-world</literal> builds a separate temporary
   installation tree for each tested module, so it requires a great deal
   more time and disk space than <literal>make installcheck-world</literal>.
  </para>

  <para>
   Alternatively, you can run individual test suites by typing
   <literal>make check</literal> or <literal>make installcheck</literal> in the appropriate
   subdirectory of the build tree.  Keep in mind that <literal>make
   installcheck</literal> assumes you've installed the relevant module(s), not
   only the core server.
  </para>

  <para>
   The additional tests that can be invoked this way include:
  </para>

  <itemizedlist>
   <listitem>
    <para>
     Regression tests for optional procedural languages (other than
     <application>PL/pgSQL</application>, which is tested by the core tests).
     These are located under <filename>src/pl</filename>.
    </para>
   </listitem>
   <listitem>
    <para>
     Regression tests for <filename>contrib</filename> modules,
     located under <filename>contrib</filename>.
     Not all <filename>contrib</filename> modules have tests.
    </para>
   </listitem>
   <listitem>
    <para>
     Regression tests for the ECPG interface library,
     located in <filename>src/interfaces/ecpg/test</filename>.
    </para>
   </listitem>
   <listitem>
    <para>
     Tests stressing behavior of concurrent sessions,
     located in <filename>src/test/isolation</filename>.
    </para>
   </listitem>
   <listitem>
    <para>
     Tests of client programs under <filename>src/bin</filename>.  See
     also <xref linkend="regress-tap"/>.
    </para>
   </listitem>
  </itemizedlist>

  <para>
   When using <literal>installcheck</literal> mode, these tests will destroy any
   existing databases named <literal>pl_regression</literal>,
   <literal>contrib_regression</literal>, <literal>isolation_regression</literal>,
   <literal>ecpg1_regression</literal>, or <literal>ecpg2_regression</literal>, as well as
   <literal>regression</literal>.
  </para>

  <para>
   The TAP-based tests are run only when PostgreSQL was configured with the
   option <option>--enable-tap-tests</option>.  This is recommended for
   development, but can be omitted if there is no suitable Perl installation.
  </para>

  <para>
   Some test suites are not run by default, either because they are not secure
   to run on a multiuser system or because they require special software.  You
   can decide which test suites to run additionally by setting the
   <command>make</command> or environment variable
   <varname>PG_TEST_EXTRA</varname> to a whitespace-separated list, for
   example:
<programlisting>
make check-world PG_TEST_EXTRA='kerberos ldap ssl'
</programlisting>
   The following values are currently supported:
   <variablelist>
    <varlistentry>
     <term><literal>kerberos</literal></term>
     <listitem>
      <para>
       Runs the test suite under <filename>src/test/kerberos</filename>.  This
       requires an MIT Kerberos installation and opens TCP/IP listen sockets.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><literal>ldap</literal></term>
     <listitem>
      <para>
       Runs the test suite under <filename>src/test/ldap</filename>.  This
       requires an <productname>OpenLDAP</productname> installation and opens
       TCP/IP listen sockets.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><literal>ssl</literal></term>
     <listitem>
      <para>
       Runs the test suite under <filename>src/test/ssl</filename>.  This opens TCP/IP listen sockets.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>

   Tests for features that are not supported by the current build
   configuration are not run even if they are mentioned in
   <varname>PG_TEST_EXTRA</varname>.
  </para>
  </sect2>

  <sect2>
   <title>Locale and Encoding</title>

   <para>
    By default, tests using a temporary installation use the
    locale defined in the current environment and the corresponding
    database encoding as determined by <command>initdb</command>.  It
    can be useful to test different locales by setting the appropriate
    environment variables, for example:
<screen>
make check LANG=C
make check LC_COLLATE=en_US.utf8 LC_CTYPE=fr_CA.utf8
</screen>
    For implementation reasons, setting <envar>LC_ALL</envar> does not
    work for this purpose; all the other locale-related environment
    variables do work.
   </para>

   <para>
    When testing against an existing installation, the locale is
    determined by the existing database cluster and cannot be set
    separately for the test run.
   </para>

   <para>
    You can also choose the database encoding explicitly by setting
    the variable <envar>ENCODING</envar>, for example:
<screen>
make check LANG=C ENCODING=EUC_JP
</screen>
    Setting the database encoding this way typically only makes sense
    if the locale is C; otherwise the encoding is chosen automatically
    from the locale, and specifying an encoding that does not match
    the locale will result in an error.
   </para>

   <para>
    The database encoding can be set for tests against either a temporary or
    an existing installation, though in the latter case it must be
    compatible with the installation's locale.
   </para>
  </sect2>

  <sect2>
   <title>Extra Tests</title>

   <para>
    The core regression test suite contains a few test files that are not
    run by default, because they might be platform-dependent or take a
    very long time to run.  You can run these or other extra test
    files by setting the variable <envar>EXTRA_TESTS</envar>.  For
    example, to run the <literal>numeric_big</literal> test:
<screen>
make check EXTRA_TESTS=numeric_big
</screen>
    To run the collation tests:
<screen>
make check EXTRA_TESTS='collate.icu.utf8 collate.linux.utf8' LANG=en_US.utf8
</screen>
    The <literal>collate.linux.utf8</literal> test works only on Linux/glibc
    platforms.  The <literal>collate.icu.utf8</literal> test only works when
    support for ICU was built.  Both tests will only succeed when run in a
    database that uses UTF-8 encoding.
   </para>
  </sect2>

  <sect2>
   <title>Testing Hot Standby</title>

  <para>
   The source distribution also contains regression tests for the static
   behavior of Hot Standby. These tests require a running primary server
   and a running standby server that is accepting new WAL changes from the
   primary (using either file-based log shipping or streaming replication).
   Those servers are not automatically created for you, nor is replication
   setup documented here. Please check the various sections of the
   documentation devoted to the required commands and related issues.
  </para>

  <para>
   To run the Hot Standby tests, first create a database
   called <literal>regression</literal> on the primary:
<screen>
psql -h primary -c "CREATE DATABASE regression"
</screen>
   Next, run the preparatory script
   <filename>src/test/regress/sql/hs_primary_setup.sql</filename>
   on the primary in the regression database, for example:
<screen>
psql -h primary -f src/test/regress/sql/hs_primary_setup.sql regression
</screen>
   Allow these changes to propagate to the standby.
  </para>

  <para>
   Now arrange for the default database connection to be to the standby
   server under test (for example, by setting the <envar>PGHOST</envar> and
   <envar>PGPORT</envar> environment variables).
   Finally, run <literal>make standbycheck</literal> in the regression directory:
<screen>
cd src/test/regress
make standbycheck
</screen>
  </para>

  <para>
   Some extreme behaviors can also be generated on the primary using the
   script <filename>src/test/regress/sql/hs_primary_extremes.sql</filename>
   to allow the behavior of the standby to be tested.
  </para>
  </sect2>
  </sect1>

  <sect1 id="regress-evaluation">
   <title>Test Evaluation</title>

   <para>
    Some properly installed and fully functional
    <productname>PostgreSQL</productname> installations can
    <quote>fail</quote> some of these regression tests due to
    platform-specific artifacts such as varying floating-point representation
    and message wording. The tests are currently evaluated using a simple
    <command>diff</command> comparison against the outputs
    generated on a reference system, so the results are sensitive to
    small system differences.  When a test is reported as
    <quote>failed</quote>, always examine the differences between
    expected and actual results; you might 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.
   </para>

   <para>
    The actual outputs of the regression tests are in files in the
    <filename>src/test/regress/results</filename> directory. The test
    script uses <command>diff</command> to compare each output
    file against the reference outputs stored in the
    <filename>src/test/regress/expected</filename> directory.  Any
    differences are saved for your inspection in
    <filename>src/test/regress/regression.diffs</filename>.
    (When running a test suite other than the core tests, these files
    of course appear in the relevant subdirectory,
    not <filename>src/test/regress</filename>.)
   </para>

   <para>
    If you don't
    like the <command>diff</command> options that are used by default, set the
    environment variable <envar>PG_REGRESS_DIFF_OPTS</envar>, for
    instance <literal>PG_REGRESS_DIFF_OPTS='-c'</literal>.  (Or you
    can run <command>diff</command> yourself, if you prefer.)
   </para>

   <para>
    If for some reason a particular platform generates a <quote>failure</quote>
    for a given test, but inspection of the output convinces you that
    the result is valid, you can add a new comparison file to silence
    the failure report in future test runs.  See
    <xref linkend="regress-variant"/> for details.
   </para>

   <sect2>
    <title>Error Message Differences</title>

    <para>
     Some of the regression tests involve intentional invalid input
     values.  Error messages can come from either the
     <productname>PostgreSQL</productname> code or from the host
     platform system routines. In the latter case, the messages can
     vary between platforms, but should reflect similar
     information. These differences in messages will result in a
     <quote>failed</quote> regression test that can be validated by
     inspection.
    </para>
   </sect2>

   <sect2>
    <title>Locale Differences</title>

    <para>
     If you run the tests against a server that was
     initialized with a collation-order locale other than C, then
     there might be differences due to sort order and subsequent
     failures.  The regression test suite is set up to handle this
     problem by providing alternate result files that together are
     known to handle a large number of locales.
    </para>

    <para>
     To run the tests in a different locale when using the
     temporary-installation method, pass the appropriate
     locale-related environment variables on
     the <command>make</command> command line, for example:
<programlisting>
make check LANG=de_DE.utf8
</programlisting>
     (The regression test driver unsets <envar>LC_ALL</envar>, so it
     does not work to choose the locale using that variable.)  To use
     no locale, either unset all locale-related environment variables
     (or set them to <literal>C</literal>) or use the following
     special invocation:
<programlisting>
make check NO_LOCALE=1
</programlisting>
     When running the tests against an existing installation, the
     locale setup is determined by the existing installation.  To
     change it, initialize the database cluster with a different
     locale by passing the appropriate options
     to <command>initdb</command>.
    </para>

    <para>
     In general, it is advisable to try to run the
     regression tests in the locale setup that is wanted for
     production use, as this will exercise the locale- and
     encoding-related code portions that will actually be used in
     production.  Depending on the operating system environment, you
     might get failures, but then you will at least know what
     locale-specific behaviors to expect when running real
     applications.
    </para>
   </sect2>

   <sect2>
    <title>Date and Time Differences</title>

    <para>
     Most of the date and time results are dependent on the time zone
     environment.  The reference files are generated for time zone
     <literal>PST8PDT</literal> (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
     <envar>PGTZ</envar> to <literal>PST8PDT</literal>, which normally
     ensures proper results.
    </para>
   </sect2>

   <sect2>
    <title>Floating-Point Differences</title>

    <para>
     Some of the tests involve computing 64-bit floating-point numbers (<type>double
     precision</type>) from table columns. Differences in
     results involving mathematical functions of <type>double
     precision</type> columns have been observed.  The <literal>float8</literal> and
     <literal>geometry</literal> tests are particularly prone to small differences
     across platforms, or even with different compiler optimization settings.
     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.
    </para>

    <para>
     Some systems display minus zero as <literal>-0</literal>, while others
     just show <literal>0</literal>.
    </para>

    <para>
     Some systems signal errors from <function>pow()</function> and
     <function>exp()</function> differently from the mechanism
     expected by the current <productname>PostgreSQL</productname>
     code.
    </para>
   </sect2>

   <sect2>
    <title>Row Ordering Differences</title>

    <para>
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 <literal>ORDER BY</literal> for every single
<literal>SELECT</literal>, and so their result row orderings are not well-defined
according to 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,
so the lack of <literal>ORDER BY</literal> is not a problem.  Some queries do exhibit
cross-platform ordering differences, however.  When testing against an
already-installed server, ordering differences can also be caused by
non-C locale settings or non-default parameter settings, such as custom values
of <varname>work_mem</varname> or the planner cost parameters.
    </para>

    <para>
Therefore, if you see an ordering difference, it's not something to
worry about, unless the query does have an <literal>ORDER BY</literal> that your
result is violating.  However, please report it anyway, so that we can add an
<literal>ORDER BY</literal> to that particular query to eliminate the bogus
<quote>failure</quote> in future releases.
    </para>

    <para>
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.
    </para>
   </sect2>

   <sect2>
    <title>Insufficient Stack Depth</title>

    <para>
     If the <literal>errors</literal> test results in a server crash
     at the <literal>select infinite_recurse()</literal> command, it means that
     the platform's limit on process stack size is smaller than the
     <xref linkend="guc-max-stack-depth"/> parameter indicates.  This
     can be fixed by running the server under a higher stack
     size limit (4MB is recommended with the default value of
     <varname>max_stack_depth</varname>).  If you are unable to do that, an
     alternative is to reduce the value of <varname>max_stack_depth</varname>.
    </para>

    <para>
     On platforms supporting <function>getrlimit()</function>, the server should
     automatically choose a safe value of <varname>max_stack_depth</varname>;
     so unless you've manually overridden this setting, a failure of this
     kind is a reportable bug.
    </para>
   </sect2>

   <sect2>
    <title>The <quote>random</quote> Test</title>

    <para>
     The <literal>random</literal> test script is intended to produce
     random results.   In very rare cases, this causes that regression
     test to fail.  Typing:
<programlisting>
diff results/random.out expected/random.out
</programlisting>
     should produce only one or a few lines of differences.  You need
     not worry unless the random test fails repeatedly.
    </para>
   </sect2>

   <sect2>
    <title>Configuration Parameters</title>

    <para>
     When running the tests against an existing installation, some non-default
     parameter settings could cause the tests to fail.  For example, changing
     parameters such as <varname>enable_seqscan</varname> or
     <varname>enable_indexscan</varname> could cause plan changes that would
     affect the results of tests that use <command>EXPLAIN</command>.
    </para>
   </sect2>
  </sect1>

<!-- We might want to move the following section into the developer's guide. -->
  <sect1 id="regress-variant">
   <title>Variant Comparison Files</title>

   <para>
    Since some of the tests inherently produce environment-dependent
    results, we have provided ways to specify alternate <quote>expected</quote>
    result files.  Each regression test can have several comparison files
    showing possible results on different platforms.  There are two
    independent mechanisms for determining which comparison file is used
    for each test.
   </para>

   <para>
    The first mechanism allows comparison files to be selected for
    specific platforms.  There is a mapping file,
    <filename>src/test/regress/resultmap</filename>, that defines
    which comparison file to use for each platform.
    To eliminate bogus test <quote>failures</quote> for a particular platform,
    you first choose or make a variant result file, and then add a line to the
    <filename>resultmap</filename> file.
   </para>

   <para>
    Each line in the mapping file is of the form
<synopsis>
testname:output:platformpattern=comparisonfilename
</synopsis>
    The test name is just the name of the particular regression test
    module. The output value indicates which output file to check. For the
    standard regression tests, this is always <literal>out</literal>. The
    value corresponds to the file extension of the output file.
    The platform pattern is a pattern in the style of the Unix
    tool <command>expr</command> (that is, a regular expression with an implicit
    <literal>^</literal> anchor at the start).  It is matched against the
    platform name as printed by <command>config.guess</command>.
    The comparison file name is the base name of the substitute result
    comparison file.
   </para>

   <para>
    For example: some systems lack a working <literal>strtof</literal> function,
    for which our workaround causes rounding errors in the
    <filename>float4</filename> regression test.
    Therefore, we provide a variant comparison file,
    <filename>float4-misrounded-input.out</filename>, which includes
    the results to be expected on these systems.  To silence the bogus
    <quote>failure</quote> message on <systemitem>HP-UX 10</systemitem>
    platforms, <filename>resultmap</filename> includes:
<programlisting>
float4:out:hppa.*-hp-hpux10.*=float4-misrounded-input.out
</programlisting>
    which will trigger on any machine where the output of
    <command>config.guess</command> matches <literal>hppa.*-hp-hpux10.*</literal>.
    Other lines in <filename>resultmap</filename> select the variant comparison
    file for other platforms where it's appropriate.
   </para>

   <para>
    The second selection mechanism for variant comparison files is
    much more automatic: it simply uses the <quote>best match</quote> among
    several supplied comparison files.  The regression test driver
    script considers both the standard comparison file for a test,
    <literal><replaceable>testname</replaceable>.out</literal>, and variant files named
    <literal><replaceable>testname</replaceable>_<replaceable>digit</replaceable>.out</literal>
    (where the <replaceable>digit</replaceable> is any single digit
    <literal>0</literal>-<literal>9</literal>).  If any such file is an exact match,
    the test is considered to pass; otherwise, the one that generates
    the shortest diff is used to create the failure report.  (If
    <filename>resultmap</filename> includes an entry for the particular
    test, then the base <replaceable>testname</replaceable> is the substitute
    name given in <filename>resultmap</filename>.)
   </para>

   <para>
    For example, for the <literal>char</literal> test, the comparison file
    <filename>char.out</filename> contains results that are expected
    in the <literal>C</literal> and <literal>POSIX</literal> locales, while
    the file <filename>char_1.out</filename> contains results sorted as
    they appear in many other locales.
   </para>

   <para>
    The best-match mechanism was devised to cope with locale-dependent
    results, but it can be used in any situation where the test results
    cannot be predicted easily from the platform name alone.  A limitation of
    this mechanism is that the test driver cannot tell which variant is
    actually <quote>correct</quote> for the current environment; it will just pick
    the variant that seems to work best.  Therefore it is safest to use this
    mechanism only for variant results that you are willing to consider
    equally valid in all contexts.
   </para>

  </sect1>

  <sect1 id="regress-tap">
   <title>TAP Tests</title>

   <para>
    Various tests, particularly the client program tests
    under <filename>src/bin</filename>, use the Perl TAP tools and are run
    using the Perl testing program <command>prove</command>.  You can pass
    command-line options to <command>prove</command> by setting
    the <command>make</command> variable <varname>PROVE_FLAGS</varname>, for example:
<programlisting>
make -C src/bin check PROVE_FLAGS='--timer'
</programlisting>
    See the manual page of <command>prove</command> for more information.
   </para>

   <para>
    The <command>make</command> variable <varname>PROVE_TESTS</varname>
    can be used to define a whitespace-separated list of paths relative
    to the <filename>Makefile</filename> invoking <command>prove</command>
    to run the specified subset of tests instead of the default
    <filename>t/*.pl</filename>.  For example:
<programlisting>
make check PROVE_TESTS='t/001_test1.pl t/003_test3.pl'
</programlisting>
   </para>

   <para>
    The TAP tests require the Perl module <literal>IPC::Run</literal>.
    This module is available from CPAN or an operating system package.
   </para>
  </sect1>

  <sect1 id="regress-coverage">
   <title>Test Coverage Examination</title>

   <para>
    The PostgreSQL source code can be compiled with coverage testing
    instrumentation, so that it becomes possible to examine which
    parts of the code are covered by the regression tests or any other
    test suite that is run with the code.  This is currently supported
    when compiling with GCC and requires the <command>gcov</command>
    and <command>lcov</command> programs.
   </para>

   <para>
    A typical workflow would look like this:
<screen>
./configure --enable-coverage ... OTHER OPTIONS ...
make
make check # or other test suite
make coverage-html
</screen>
    Then point your HTML browser
    to <filename>coverage/index.html</filename>.
    The <command>make</command> commands also work in subdirectories.
   </para>

   <para>
    If you don't have <command>lcov</command> or prefer text output over an
    HTML report, you can also run
<screen>
make coverage
</screen>
    instead of <literal>make coverage-html</literal>, which will
    produce <filename>.gcov</filename> output files for each source file
    relevant to the test.  (<literal>make coverage</literal> and <literal>make
    coverage-html</literal> will overwrite each other's files, so mixing them
    might be confusing.)
   </para>

   <para>
    To reset the execution counts between test runs, run:
<screen>
make coverage-clean
</screen>
   </para>
  </sect1>

</chapter>
