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       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

         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

       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

   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

         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 ( 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:

         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
       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:

           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

       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

       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

         package My::TAP::Harness;

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

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


       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;
         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

       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:


       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


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

         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
       ( for an example of this

   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

       [1] <> [2]
       <> [3]

perl v5.24.0                      2016-03-01         TAP::Harness::Beyond(3pm)

perl 5.24 - Generated Wed Nov 23 18:12:58 CST 2016
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