phpman > perldoc > TAP::Harness::Beyond(3perl)

NAME
    Test::Harness::Beyond - Beyond make test

Beyond make test
    Test::Harness is responsible for running test scripts, analysing their output and reporting
    success or failure. When I type make test (or ./Build test) for a module, Test::Harness is
    usually used to run the tests (not all modules use Test::Harness but the majority do).

    To start exploring some of the features of Test::Harness I need to switch from make test to the
    prove command (which ships with Test::Harness). For the following examples I'll also need a
    recent version of Test::Harness installed; 3.14 is current as I write.

    For the examples I'm going to assume that we're working with a 'normal' Perl module
    distribution. Specifically I'll assume that typing make or ./Build causes the built,
    ready-to-install module code to be available below ./blib/lib and ./blib/arch and that there's a
    directory called 't' that contains our tests. Test::Harness isn't hardwired to that
    configuration but it saves me from explaining which files live where for each example.

    Back to prove; like make test it runs a test suite - but it provides far more control over which
    tests are executed, in what order and how their results are reported. Typically make test runs
    all the test scripts below the 't' directory. To do the same thing with prove I type:

      prove -rb t

    The switches here are -r to recurse into any directories below 't' and -b which adds ./blib/lib
    and ./blib/arch to Perl's include path so that the tests can find the code they will be testing.
    If I'm testing a module of which an earlier version is already installed I need to be careful
    about the include path to make sure I'm not running my tests against the installed version
    rather than the new one that I'm working on.

    Unlike make test, typing prove doesn't automatically rebuild my module. If I forget to make
    before prove I will be testing against older versions of those files - which inevitably leads to
    confusion. I either get into the habit of typing

      make && prove -rb t

    or - if I have no XS code that needs to be built I use the modules below lib instead

      prove -Ilib -r t

    So far I've shown you nothing that make test doesn't do. Let's fix that.

  Saved State
    If I have failing tests in a test suite that consists of more than a handful of scripts and
    takes more than a few seconds to run it rapidly becomes tedious to run the whole test suite
    repeatedly as I track down the problems.

    I can tell prove just to run the tests that are failing like this:

      prove -b t/this_fails.t t/so_does_this.t

    That speeds things up but I have to make a note of which tests are failing and make sure that I
    run those tests. Instead I can use prove's --state switch and have it keep track of failing
    tests for me. First I do a complete run of the test suite and tell prove to save the results:

      prove -rb --state=save t

    That stores a machine readable summary of the test run in a file called '.prove' in the current
    directory. If I have failures I can then run just the failing scripts like this:

      prove -b --state=failed

    I can also tell prove to save the results again so that it updates its idea of which tests
    failed:

      prove -b --state=failed,save

    As soon as one of my failing tests passes it will be removed from the list of failed tests.
    Eventually I fix them all and prove can find no failing tests to run:

      Files=0, Tests=0, 0 wallclock secs ( 0.00 usr + 0.00 sys = 0.00 CPU)
      Result: NOTESTS

    As I work on a particular part of my module it's most likely that the tests that cover that code
    will fail. I'd like to run the whole test suite but have it prioritize these 'hot' tests. I can
    tell prove to do this:

      prove -rb --state=hot,save t

    All the tests will run but those that failed most recently will be run first. If no tests have
    failed since I started saving state all tests will run in their normal order. This combines full
    test coverage with early notification of failures.

    The --state switch supports a number of options; for example to run failed tests first followed
    by all remaining tests ordered by the timestamps of the test scripts - and save the results - I
    can use

      prove -rb --state=failed,new,save t

    See the prove documentation (type prove --man) for the full list of state options.

    When I tell prove to save state it writes a file called '.prove' ('_prove' on Windows) in the
    current directory. It's a YAML document so it's quite easy to write tools of your own that work
    on the saved test state - but the format isn't officially documented so it might change without
    (much) warning in the future.

  Parallel Testing
    If my tests take too long to run I may be able to speed them up by running multiple test scripts
    in parallel. This is particularly effective if the tests are I/O bound or if I have multiple CPU
    cores. I tell prove to run my tests in parallel like this:

      prove -rb -j 9 t

    The -j switch enables parallel testing; the number that follows it is the maximum number of
    tests to run in parallel. Sometimes tests that pass when run sequentially will fail when run in
    parallel. For example if two different test scripts use the same temporary file or attempt to
    listen on the same socket I'll have problems running them in parallel. If I see unexpected
    failures I need to check my tests to work out which of them are trampling on the same resource
    and rename temporary files or add locks as appropriate.

    To get the most performance benefit I want to have the test scripts that take the longest to run
    start first - otherwise I'll be waiting for the one test that takes nearly a minute to complete
    after all the others are done. I can use the --state switch to run the tests in slowest to
    fastest order:

      prove -rb -j 9 --state=slow,save t

  Non-Perl Tests
    The Test Anything Protocol (http://testanything.org/) isn't just for Perl. Just about any
    language can be used to write tests that output TAP. There are TAP based testing libraries for
    C, C++, PHP, Python and many others. If I can't find a TAP library for my language of choice
    it's easy to generate valid TAP. It looks like this:

      1..3
      ok 1 - init OK
      ok 2 - opened file
      not ok 3 - appended to file

    The first line is the plan - it specifies the number of tests I'm going to run so that it's easy
    to check that the test script didn't exit before running all the expected tests. The following
    lines are the test results - 'ok' for pass, 'not ok' for fail. Each test has a number and,
    optionally, a description. And that's it. Any language that can produce output like that on
    STDOUT can be used to write tests.

    Recently I've been rekindling a two-decades-old interest in Forth. Evidently I have a
    masochistic streak that even Perl can't satisfy. I want to write tests in Forth and run them
    using prove (you can find my gforth TAP experiments at
    https://svn.hexten.net/andy/Forth/Testing/). I can use the --exec switch to tell prove to run
    the tests using gforth like this:

      prove -r --exec gforth t

    Alternately, if the language used to write my tests allows a shebang line I can use that to
    specify the interpreter. Here's a test written in PHP:

      #!/usr/bin/php
      <?php
        print "1..2\n";
        print "ok 1\n";
        print "not ok 2\n";
      ?>

    If I save that as t/phptest.t the shebang line will ensure that it runs correctly along with all
    my other tests.

  Mixing it up
    Subtle interdependencies between test programs can mask problems - for example an earlier test
    may neglect to remove a temporary file that affects the behaviour of a later test. To find this
    kind of problem I use the --shuffle and --reverse options to run my tests in random or reversed
    order.

  Rolling My Own
    If I need a feature that prove doesn't provide I can easily write my own.

    Typically you'll want to change how TAP gets *input* into and *output* from the parser.
    App::Prove supports arbitrary plugins, and TAP::Harness supports custom *formatters* and *source
    handlers* that you can load using either prove or Module::Build; there are many examples to base
    mine on. For more details see App::Prove, TAP::Parser::SourceHandler, and TAP::Formatter::Base.

    If writing a plugin is not enough, you can write your own test harness; one of the motives for
    the 3.00 rewrite of Test::Harness was to make it easier to subclass and extend.

    The Test::Harness module is a compatibility wrapper around TAP::Harness. For new applications I
    should use TAP::Harness directly. As we'll see, prove uses TAP::Harness.

    When I run prove it processes its arguments, figures out which test scripts to run and then
    passes control to TAP::Harness to run the tests, parse, analyse and present the results. By
    subclassing TAP::Harness I can customise many aspects of the test run.

    I want to log my test results in a database so I can track them over time. To do this I override
    the summary method in TAP::Harness. I start with a simple prototype that dumps the results as a
    YAML document:

      package My::TAP::Harness;

      use base 'TAP::Harness';
      use YAML;

      sub summary {
        my ( $self, $aggregate ) = @_;
        print Dump( $aggregate );
        $self->SUPER::summary( $aggregate );
      }

      1;

    I need to tell prove to use my My::TAP::Harness. If My::TAP::Harness is on Perl's @INC include
    path I can

      prove --harness=My::TAP::Harness -rb t

    If I don't have My::TAP::Harness installed on @INC I need to provide the correct path to perl
    when I run prove:

      perl -Ilib `which prove` --harness=My::TAP::Harness -rb t

    I can incorporate these options into my own version of prove. It's pretty simple. Most of the
    work of prove is handled by App::Prove. The important code in prove is just:

      use App::Prove;

      my $app = App::Prove->new;
      $app->process_args(@ARGV);
      exit( $app->run ? 0 : 1 );

    If I write a subclass of App::Prove I can customise any aspect of the test runner while
    inheriting all of prove's behaviour. Here's myprove:

      #!/usr/bin/env perl use lib qw( lib );      # Add ./lib to @INC
      use App::Prove;

      my $app = App::Prove->new;

      # Use custom TAP::Harness subclass
      $app->harness( 'My::TAP::Harness' );

      $app->process_args( @ARGV ); exit( $app->run ? 0 : 1 );

    Now I can run my tests like this

      ./myprove -rb t

  Deeper Customisation
    Now that I know how to subclass and replace TAP::Harness I can replace any other part of the
    harness. To do that I need to know which classes are responsible for which functionality. Here's
    a brief guided tour; the default class for each component is shown in parentheses. Normally any
    replacements I write will be subclasses of these default classes.

    When I run my tests TAP::Harness creates a scheduler (TAP::Parser::Scheduler) to work out the
    running order for the tests, an aggregator (TAP::Parser::Aggregator) to collect and analyse the
    test results and a formatter (TAP::Formatter::Console) to display those results.

    If I'm running my tests in parallel there may also be a multiplexer (TAP::Parser::Multiplexer) -
    the component that allows multiple tests to run simultaneously.

    Once it has created those helpers TAP::Harness starts running the tests. For each test it
    creates a new parser (TAP::Parser) which is responsible for running the test script and parsing
    its output.

    To replace any of these components I call one of these harness methods with the name of the
    replacement class:

      aggregator_class
      formatter_class
      multiplexer_class
      parser_class
      scheduler_class

    For example, to replace the aggregator I would

      $harness->aggregator_class( 'My::Aggregator' );

    Alternately I can supply the names of my substitute classes to the TAP::Harness constructor:

      my $harness = TAP::Harness->new(
        { aggregator_class => 'My::Aggregator' }
      );

    If I need to reach even deeper into the internals of the harness I can replace the classes that
    TAP::Parser uses to execute test scripts and tokenise their output. Before running a test script
    TAP::Parser creates a grammar (TAP::Parser::Grammar) to decode the raw TAP into tokens, a result
    factory (TAP::Parser::ResultFactory) to turn the decoded TAP results into objects and, depending
    on whether it's running a test script or reading TAP from a file, scalar or array a source or an
    iterator (TAP::Parser::IteratorFactory).

    Each of these objects may be replaced by calling one of these parser methods:

      source_class
      perl_source_class
      grammar_class
      iterator_factory_class
      result_factory_class

  Callbacks
    As an alternative to subclassing the components I need to change I can attach callbacks to the
    default classes. TAP::Harness exposes these callbacks:

      parser_args      Tweak the parameters used to create the parser
      made_parser      Just made a new parser
      before_runtests  About to run tests
      after_runtests   Have run all tests
      after_test       Have run an individual test script

    TAP::Parser also supports callbacks; bailout, comment, plan, test, unknown, version and yaml are
    called for the corresponding TAP result types, ALL is called for all results, ELSE is called for
    all results for which a named callback is not installed and EOF is called once at the end of
    each TAP stream.

    To install a callback I pass the name of the callback and a subroutine reference to TAP::Harness
    or TAP::Parser's callback method:

      $harness->callback( after_test => sub {
        my ( $script, $desc, $parser ) = @_;
      } );

    I can also pass callbacks to the constructor:

      my $harness = TAP::Harness->new({
        callbacks => {
                after_test => sub {
            my ( $script, $desc, $parser ) = @_;
            # Do something interesting here
                }
        }
      });

    When it comes to altering the behaviour of the test harness there's more than one way to do it.
    Which way is best depends on my requirements. In general if I only want to observe test
    execution without changing the harness' behaviour (for example to log test results to a
    database) I choose callbacks. If I want to make the harness behave differently subclassing gives
    me more control.

  Parsing TAP
    Perhaps I don't need a complete test harness. If I already have a TAP test log that I need to
    parse all I need is TAP::Parser and the various classes it depends upon. Here's the code I need
    to run a test and parse its TAP output

      use TAP::Parser;

      my $parser = TAP::Parser->new( { source => 't/simple.t' } );
      while ( my $result = $parser->next ) {
        print $result->as_string, "\n";
      }

    Alternately I can pass an open filehandle as source and have the parser read from that rather
    than attempting to run a test script:

      open my $tap, '<', 'tests.tap'
        or die "Can't read TAP transcript ($!)\n";
      my $parser = TAP::Parser->new( { source => $tap } );
      while ( my $result = $parser->next ) {
        print $result->as_string, "\n";
      }

    This approach is useful if I need to convert my TAP based test results into some other
    representation. See TAP::Convert::TET (http://search.cpan.org/dist/TAP-Convert-TET/) for an
    example of this approach.

  Getting Support
    The Test::Harness developers hang out on the tapx-dev mailing list[1]. For discussion of
    general, language independent TAP issues there's the tap-l[2] list. Finally there's a wiki
    dedicated to the Test Anything Protocol[3]. Contributions to the wiki, patches and suggestions
    are all welcome.

    [1] <http://www.hexten.net/mailman/listinfo/tapx-dev> [2]
    <http://testanything.org/mailman/listinfo/tap-l> [3] <http://testanything.org/>