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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/>