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Test::Trap::Builder(3)               User Contributed Perl Documentation              Test::Trap::Builder(3)



NAME
       Test::Trap::Builder - Backend for building test traps

VERSION
       Version 0.2.2

SYNOPSIS
         package My::Test::Trap;

         use Test::Trap::Builder;
         my $B = Test::Trap::Builder->new;

         $B->layer( $layer_name => \&layer_implementation );
         $B->accessor( simple => [ $layer_name ] );

         $B->multi_layer( $multi_name => @names );

         $B->test( $test_name => 'trap, predicate, name', \&test_function );

DESCRIPTION
       Test::Trap neither traps nor tests everything you may want to trap or test.  So, Test::Trap::Builder
       provides methods to write your own trap layers, accessors, and test callbacks -- preferably for use
       with your own modules (trappers).

       Note that layers are methods with mangled names (names are prefixed with "layer:"), and so inherited
       like any other method, while accessors are ordinary methods.  Meanwhile, test callbacks are not
       referenced in the symbol table by themselves, but only in combinations with accessors, all methods of
       the form ACCESSOR_TEST.

EXPORTS
       Trappers should not inherit from Test::Trap::Builder, but may import a few convenience methods for
       use in building the trap.  Do not use them as methods of Test::Trap::Builder -- they are intended to
       be methods of trap objects.  (If you inherit from another trapper, you need not, and probably should
       not, import these yourself -- you should inherit these methods like any other.)

       Trappers may import any number of these methods, or all of them by way of the ":methods" tag.

       Layers should be implemented as methods, and while they need not call any of these convenience
       methods in turn, that likely makes for more readable code than any alternative.  Likewise, test
       callbacks may use convenience methods for more readable code.

       Of course, certain convenience methods may also be useful in more generic methods messing with trap
       or builder objects.

   Prop [PACKAGE]
       A method returning a reference to a hash, holding the PACKAGE's (by default the caller's) tag-on
       properties for the (current) trap object.  Currently, Test::Trap::Builder defines the following
       properties:

       layers
           While the trap is springing, the queue of layers remaining.  Usually set by the "trap" method and
           consumed by the "Next" method.

       teardown
           While the trap is springing, the queue of teardown actions remaining.  Usually accumulated
           through the "Teardown" method and invoked by the "trap" method.

       code
           The user code trapped.  Usually set by the "trap" method and invoked by the "Run" method.

       exception
           An internal exception.  Usually set through the "Exception" method and examined by the "trap"
           method.

       on_test_failure
           A callback invoked by the "TestFailure" method.  Layers in particular may want to set this.

       test_accessor
           The name and (optionally) the index of the accessor, the contents of which we're currently
           testing.  Best accessed through the "TestAccessor" method, and usually set by the "test" and
           "accessor" methods, but if you are writing your own tests or accessors directly, you just might
           need to set it.  Perhaps.

       Be nice: Treat another module's tag-on properties as you would treat another module's global
       variables.  Don't use them except as documented.

       Example:

         # in a layer, setting the callback for TestFailure:
         $self->Prop('Test::Trap::Builder')->{on_test_failure} = \&mydiag;

   DESTROY
       This cleans up the tag-on properties when the trap object is destroyed.  Don't try to make a trapper
       that doesn't call this; it will get confused.

       If your trapper needs its own "DESTROY", make sure it calls this one as well:

         sub DESTROY {
           my $self = shift;
           # do your thing
           $self->Test::Trap::Builder::DESTROY;
           # and more things
         }

   Run
       A terminating layer should call this method to run the user code.  Should only be called in a dynamic
       context in which layers are being applied.

   Next
       Every non-terminating layer should call this method (or an equivalent) to progress to the next layer.
       Should only be called in a dynamic context in which layers are being applied.  Note that this method
       need not return, so any tear-down actions should probably be registered with the Teardown method (see
       below).

   Teardown SUBS
       If your layer wants to clean up its setup, it may use this method to register any number of tear-down
       actions, to be performed (in reverse registration order) once the user code has been executed.
       Should only be called in a dynamic context in which layers are being applied.

   TestAccessor
       Returns a string of the form "NAME(INDEX)", where NAME and INDEX are the name of the accessor and the
       index (if any) being tested.  Should only be called in the dynamic context of test callbacks.

       This is intended for diagnostics:

         diag( sprintf 'Expected %s in %s; got %s',
               $expected, $self->TestAccessor, dump($got),
             );

   TestFailure
       Runs the "on_test_failure" tag-on property (if any) on the trap object.  If you are writing
       unregistered tests, you might want to include (some variation of) this call:

         $ok or $self->TestFailure;

   Exception STRINGS
       Layer implementations may run into exceptional situations, in which they want the entire trap to
       fail.  Unfortunately, another layer may be trapping ordinary exceptions, so you need some kind of
       magic in order to throw an untrappable exception.  This is one convenient way.

       Should only be called in a dynamic context in which layers are being applied.

       Note: The Exception method won't work if called from outside of the regular control flow, like inside
       a DESTROY method or signal handler.  If anything like this happens, CORE::exit will be called with an
       exit code of 8.

METHODS
   new
       Returns a singleton object.  Don't expect this module to work with a different instance object of
       this class.

   trap TRAPPER, GLOBREF, LAYERARRAYREF, CODE
       Implements a trap for the TRAPPER module, applying the layers of LAYERARRAYREF, trapping various
       outcomes of the user CODE, and storing the trap object into the scalar slot of GLOBREF.

       In most cases, the trapper should conveniently export a function calling this method.

   layer NAME, CODE
       Registers a layer by NAME to the calling trapper.  When the layer is applied, the CODE will be
       invoked on the trap object being built, with no arguments, and should call either the Next() or Run()
       method or equivalent.

   output_layer NAME, GLOBREF
       Registers (by NAME and to the calling trapper) a layer for trapping output on the file handle of the
       GLOBREF, using NAME also as the attribute name.

   output_layer_backend NAME, [CODE]
       When called with two arguments, registers (by NAME and globally) a backend for output trap layers.
       When called with a single argument, looks up and returns the backend registered by NAME (or undef).

       When a layer using this backend is applied, the CODE will be called on the trap object, with the
       layer name and the output handle's fileno and globref as arguments.

   first_output_layer_backend SPEC
       Where SPEC is empty, just returns.

       Where SPEC is a string of comma-or-semicolon separated backend names, runs through the names,
       returning the first implementation it finds.  Dies if no implementation is found by any of these
       names.

   multi_layer NAME, LAYERS
       Registers (by NAME) a layer that just pushes a number of other LAYERS on the stack of layers.  If any
       of the LAYERS is neither an anonymous method nor the name of a layer registered to the caller or a
       trapper it inherits from, an exception is raised.

   layer_implementation TRAPPER, LAYERS
       Returns the subroutines that implement the requested LAYERS.  If any of the LAYERS is neither an
       anonymous method nor the name of a layer registered to or inherited by the TRAPPER, an exception is
       raised.

   accessor NAMED_ARGS
       Generates and registers any number of accessors according to the NAMED_ARGS, and also generates the
       proper test methods for these accessors (see below).

       The following named arguments are recognized:

       is_leaveby
           If true, the tests methods will generate better diagnostics if the trap was not left as
           specified.  Also, a special did_ACCESSOR test method will be generated (unless already present),
           simply passing as long as the trap was left as specified.

       is_array
           If true, the simple accessor(s) will be smart about context and arguments, returning an arrayref
           on no argument (in any context), an array slice in list context (on any number of arguments), and
           the element indexed by the first argument otherwise.

       simple
           Should be a reference to an array of accessor names.  For each name, an accessor (assuming hash
           based trap object with accessor names as keys), will be generated and registered.

       flexible
           Should be a reference to a hash.  For each pair, a name and an implementation, an accessor is
           generated and registered.

   test NAME, ARGSPEC, CODE
       Registers a test callback by NAME and to the calling trapper.

       Trappers inherit test callbacks like methods (though they are not implemented as such; don't expect
       to find them in the symbol table).

       Test methods of the form ACCESSOR_TEST will be made available (directly or by inheritence) to every
       trapper that registers or inherits both the accessor named ACCESSOR and the test named TEST.

       (In more detail, the method will be generated in every trapper that either (1) registers both the
       test and the accessor, or (2) registers either and inherits the other.)

       When the test method is called, any implicit leaveby condition will be tested first, and if it passes
       (or there were none), the CODE is called with arguments according to the words found in the ARGSPEC
       string:

       trap
           The trap object.

       entirety
           The ACCESSOR's return value when called without arguments.

       element
           The ACCESSOR's return value when called with index, if applicable (i.e. for array accessors).
           Index is not applicable to scalar accessors, so such are still called without index.

           The index, when applicable, will be taken from the test method's arguments.

       predicate
           What the ACCESSOR's return value should be tested against (taken from the test method's
           arguments).  (There may be any fixed number of predicates.)

       name
           The test name (taken from the test method's arguments).

EXAMPLE
       A complete example, implementing a timeout layer (depending on Time::HiRes::ualarm being present), a
       simpletee layer (printing the trapped stdout/stderr to the original file handles after the trap has
       sprung), and a cmp_ok test method template:

         package My::Test::Trap;
         use base 'Test::Trap'; # for example
         use Test::Trap::Builder;

         my $B = Test::Trap::Builder->new;

         # example (layer:timeout):
         use Time::HiRes qw/ualarm/;
         $B->layer( timeout => $_ ) for sub {
           my $self = shift;
           eval {
             local $SIG{ALRM} = sub {
               $self->{timeout} = 1; # simple truth
               $SIG{ALRM} = sub {die};
               die;
             };
             ualarm 1000, 1; # one second max, then die repeatedly!
             $self->Next;
           };
           alarm 0;
           if ($self->{timeout}) {
             $self->{leaveby} = 'timeout';
             delete $self->{$_} for qw/ die exit return /;
           }
         };
         $B->accessor( is_leaveby => 1,
                       simple => ['timeout'],
                     );

         # example (layer:simpletee):
         $B->layer( simpletee => $_ ) for sub {
           my $self = shift;
           for (qw/ stdout stderr /) {
             exists $self->{$_} or $self->Exception("Too late to tee $_");
           }
           $self->Teardown($_) for sub {
             print STDOUT $self->{stdout} if exists $self->{stdout};
             print STDERR $self->{stderr} if exists $self->{stderr};
           };
           $self->Next;
         };
         # no accessor for this layer

         $B->multi_layer( flow => qw/ raw die exit timeout / );
         $B->multi_layer( default => qw/ flow stdout stderr warn simpletee / );

         $B->test_method( cmp_ok => 1, 2, \&Test::More::cmp_ok );

CAVEATS
       The interface of this module is likely to remain somewhat in flux for a while yet.

       The different implementations of output trap layers have their own caveats; see
       Test::Trap::Builder::Tempfile, Test::Trap::Builder::PerlIO, Test::Trap::Builder::SystemSafe.

       Multiple inheritance is not (yet?) fully supported.  If one parent has registered a test callback "X"
       and another has registered an accessor "Y", the test method "Y_X" will not be generated.

       Threads?  No idea.  It might even work correctly.

BUGS
       Please report any bugs or feature requests directly to the author.

AUTHOR
       Eirik Berg Hanssen, "<ebhanssen@allverden.no>"

COPYRIGHT & LICENSE
       Copyright 2006-2012 Eirik Berg Hanssen, All Rights Reserved.

       This program is free software; you can redistribute it and/or modify it under the same terms as Perl
       itself.



perl v5.16.2                                     2013-08-25                           Test::Trap::Builder(3)