TAP::Harness::Beyond(3p) Perl Programmers Reference Guide #
TAP::Harness::Beyond(3p) Perl Programmers Reference Guide
NNAAMMEE #
Test::Harness::Beyond - Beyond make test
BBeeyyoonndd mmaakkee tteesstt Test::Harness is responsible for running test scripts, analysing their output and reporting success or failure. When I type _m_a_k_e _t_e_s_t (or _._/_B_u_i_l_d _t_e_s_t) 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 _m_a_k_e _t_e_s_t to the _p_r_o_v_e 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 _m_a_k_e or
_._/_B_u_i_l_d 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 _p_r_o_v_e; like _m_a_k_e _t_e_s_t 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 _m_a_k_e _t_e_s_t 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 _m_a_k_e _t_e_s_t, typing _p_r_o_v_e 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
_l_i_b instead
prove -Ilib -r t
So far I've shown you nothing that _m_a_k_e _t_e_s_t doesn't do. Let's fix that.
SSaavveedd SSttaattee 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.
PPaarraalllleell TTeessttiinngg 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
NNoonn--PPeerrll TTeessttss 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.
MMiixxiinngg iitt uupp 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.
RRoolllliinngg MMyy OOwwnn 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 _i_n_p_u_t into and _o_u_t_p_u_t from
the parser. App::Prove supports arbitrary plugins, and TAP::Harness
supports custom _f_o_r_m_a_t_t_e_r_s and _s_o_u_r_c_e _h_a_n_d_l_e_r_s 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
DDeeeeppeerr CCuussttoommiissaattiioonn 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
CCaallllbbaacckkss 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.
PPaarrssiinngg TTAAPP 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.
GGeettttiinngg SSuuppppoorrtt 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/>
perl v5.36.3 2017-02-05 TAP::Harness::Beyond(3p)