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TAP::Harness::Beyond(3pm)             Perl Programmers Reference Guide             TAP::Harness::Beyond(3pm)



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



perl v5.16.2                                     2012-10-11                        TAP::Harness::Beyond(3pm)