Test::Trap(3) User Contributed Perl Documentation Test::Trap(3)NAME
Test::Trap - Trap exit codes, exceptions, output, etc.
VERSION
Version 0.2.2
SYNOPSIS
use Test::More;
use Test::Trap;
my @r = trap { some_code(@some_parameters) };
is ( $trap->exit, 1, 'Expecting &some_code to exit with 1' );
is ( $trap->stdout, '', 'Expecting no STDOUT' );
like ( $trap->stderr, qr/^Bad parameters; exiting\b/, 'Expecting warnings.' );
DESCRIPTION
Primarily (but not exclusively) for use in test scripts: A block eval
on steroids, configurable and extensible, but by default trapping
(Perl) STDOUT, STDERR, warnings, exceptions, would-be exit codes, and
return values from boxed blocks of test code.
The values collected by the latest trap can then be queried or tested
through a special trap object.
EXPORT
A function and a scalar may be exported by any name. The function (by
default named "trap") is an analogue to block eval(), and the scalar
(by default named $trap) is the corresponding analogue to $@.
Optionally, you may specify the layers of the exported trap. Layers
may be specified by name, with a colon sigil. Multiple layers may be
given in a list, or just stringed together like ":flow:stderr:warn".
(For the advanced user, you may also specify anonymous layer
implementations -- i.e. an appropriate subroutine.)
See below for a list of the built-in layers, most of which are enabled
by default. Note, finally, that the ordering of the layers matter: The
:raw layer is always on the bottom (anything underneath it is ignored),
and any other "flow control" layers used should be right down there
with it.
FUNCTION
trap BLOCK
This function may be exported by any name, but defaults to "trap".
By default, traps exceptions (like block eval), but also exits and exit
codes, returns and return values, context, and (Perl) output on STDOUT
or STDERR, and warnings. All information trapped can be queried
through the trap object, which is by default exported as $trap, but can
be exported by any name.
The value returned from "trap" mimics that returned from "eval": If
the BLOCK would die or exit, it returns an undefined value in scalar
context or an empty list in list context; otherwise it returns whatever
the BLOCK would return in the given context (also available as the
trapped return values).
TRAP LAYERS
Exactly what the "trap" traps depends on the layers of the trap. It is
possible to register more (see Test::Trap::Builder), but the following
layers are pre-defined by this module:
:raw
The terminating layer, at which the processing of the layers stops, and
the actual call to the user code is performed. On success, it collects
the return value(s) in the appropriate context. Pushing the :raw layer
on a trap will for most purposes remove all layers below.
:die
The layer emulating block eval, capturing normal exceptions.
:exit
The third "flow control" layer, capturing exit codes if anything used
in the dynamic scope of the trap calls CORE::GLOBAL::exit(). (See
CAVEATS below for more.)
:flow
A pseudo-layer shortcut for :raw:die:exit. Since this includes :raw,
pushing :flow on a trap will remove all layers below.
:stdout, :stderr
Layers trapping Perl output on STDOUT and STDERR, respectively.
:stdout(perlio), :stderr(perlio)
As above, but specifying a backend implemented using PerlIO::scalar.
If this backend is not available (typically if PerlIO is not), this is
an error.
:stdout(tempfile), :stderr(tempfile)
As above, but specifying a backend implemented using File::Temp. Note
that this is the default implementation, unless the ":output()" layer
is used to set another default.
:stdout(a;b;c), :stderr(a,b,c)
(Either syntax, commas or semicolons, is permitted, as is any number of
names in the list.) As above, but specifying the backend
implementation by the first existing name among a, b, and c. If no
such implementation is available, this is an error.
:warn
A layer trapping warnings, with additional tee: If STDERR is open, it
will also print the warnings there. (This output may be trapped by the
:stderr layer, be it above or below the :warn layer.)
:default
A pseudo-layer short-cut for :raw:die:exit:stdout:stderr:warn. Since
this includes :raw, pushing :default on a trap will remove all layers
below. The other interesting property of :default is that it is what
every trap starts with: In order not to include any of the six layers
that make up :default, you need to push a terminating layer (such as
:raw or :flow) on the trap.
:on_fail(m)
A (non-default) pseudo-layer that installs a callback method (by name)
m to be run on test failures. To run the "diag_all" method every time
a test fails:
use Test::Trap qw/ :on_fail(diag_all) /;
:void, :scalar, :list
Runs the trapped user code in void, scalar, or list context,
respectively. (By default, the code is run in whatever context the
trap itself is in.)
If more than one of these layers are pushed on the trap, the deepest
(that is, leftmost) takes precedence:
use Test::Trap qw/ :scalar:void:list /;
trap { 42, 13 };
$trap->return_is_deeply( [ 13 ], 'Scalar comma.' );
:output(a;b;c)
A (non-default) pseudo-layers that sets the default backend layer
implementation for any output trapping (":stdout", ":stderr", or other
similarly defined) layers already on the trap.
use Test::Trap qw/ :output(systemsafe) /;
trap { system echo => 'Hello Unix!' }; # trapped!
RESULT ACCESSORS
The following methods may be called on the trap objects after any trap
has been sprung, and access the outcome of the run.
Any property will be undef if not actually trapped -- whether because
there is no layer to trap them or because flow control passed them by.
(If there is an active and successful trap layer, empty strings and
empty arrays trapped will of course be defined.)
When properties are set, their values will be as follows:
leaveby
A string indicating how the trap terminated: "return", "die", or
"exit".
die
The exception, if the latest trap threw one.
exit
The exit code, if the latest trap tried to exit.
return [INDEX ...]
Returns undef if the latest trap did not terminate with a return;
otherwise returns three different views of the return array:
· if no INDEX is passed, returns a reference to the array (NB! an
empty array of indices qualifies as "no index")
· if called with at least one INDEX in scalar context, returns the
array element indexed by the first INDEX (ignoring the rest)
· if called with at least one INDEX in list context, returns the
slice of the array by these indices
Note: The array will hold but a single value if the trap was sprung in
scalar context, and will be empty if it was in void context.
stdout, stderr
The captured output on the respective file handles.
warn [INDEX]
Returns undef if the latest trap had no warning-trapping layer;
otherwise returns three different views of the warn array:
· if no INDEX is passed, returns a reference to the array (NB! an
empty array of indices qualifies as "no index")
· if called with at least one INDEX in scalar context, returns the
array element indexed by the first INDEX (ignoring the rest)
· if called with at least one INDEX in list context, returns the
slice of the array by these indices
wantarray
The context in which the latest code trapped was called. (By default a
propagated context, but layers can override this.)
list, scalar, void
True if the latest code trapped was called in the indicated context.
(By default the code will be called in a propagated context, but layers
can override this.)
RESULT TESTS
For each accessor, a number of convenient standard test methods are
also available. By default, these are a few standard tests from
Test::More, plus the "nok" test (a negated "ok" test). All for
convenience:
ACCESSOR_ok [INDEX,] TEST_NAME
ACCESSOR_nok [INDEX,] TEST_NAME
ACCESSOR_is [INDEX,] SCALAR, TEST_NAME
ACCESSOR_isnt [INDEX,] SCALAR, TEST_NAME
ACCESSOR_isa_ok [INDEX,] SCALAR, INVOCANT_NAME
ACCESSOR_like [INDEX,] REGEX, TEST_NAME
ACCESSOR_unlike [INDEX,] REGEX, TEST_NAME
ACCESSOR_is_deeply STRUCTURE, TEST_NAME
INDEX is not optional: It is required for array accessors (like
"return" and "warn"), and disallowed for scalar accessors. Note that
the "is_deeply" test does not accept an index. Even for array
accessors, it operates on the entire array.
For convenience and clarity, tests against a flow control ACCESSOR
("return", "die", "exit", or any you define yourself) will first test
whether the trap was left by way of the flow control mechanism in
question, and fail with appropriate diagnostics otherwise.
did_die, did_exit, did_return
Conveniences: Tests whether the trap was left by way of the flow
control mechanism in question. Much like "leaveby_is('die')" etc, but
with better diagnostics and (run-time) spell checking.
quiet
Convenience: Passes if zero-length output was trapped on both STDOUT
and STDERR, and generate better diagnostics otherwise.
UTILITIES
diag_all
Prints a diagnostic message (as per "diag" in Test::More) consisting of
a dump (in Perl code, as per Data::Dump) of the trap object.
diag_all_once
As "diag_all", except if this instance of the trap object has already
been diag_all_once'd, the diagnostic message will instead consist of
the string "(as above)".
This could be useful with the "on_fail" layer:
use Test::Trap qw/ :on_fail(diag_all_once) /;
CAVEATS
This module must be loaded before any code containing exit()s to be
trapped is compiled. Any exit() already compiled won't be trappable,
and will terminate the program anyway.
This module overrides &CORE::GLOBAL::exit, so may not work correctly
(or even at all) in the presence of other code overriding
&CORE::GLOBAL::exit. More precisely: This module installs its own
exit() on entry of the block, and restores the previous one, if any,
only upon leaving the block.
If you use fork() in the dynamic scope of a trap, beware that the
(default) :exit layer of that trap does not trap exit() in the
children, but passes them to the outer handler. If you think about it,
this is what you are likely to want it to do in most cases.
Note that the (default) :exit layer only traps &CORE::GLOBAL::exit
calls (and bare exit() calls that compile to that). It makes no
attempt to trap CORE::exit(), POSIX::_exit(), exec(), nor segfault.
Nor does it attempt to trap anything else that might terminate the
program. The trap is a block eval on steroids -- not the last block
eval of Krypton!
This module traps warnings using $SIG{__WARN__}, so may not work
correctly (or even at all) in the presence of other code setting this
handler. More precisely: This module installs its own __WARN__ handler
on entry of the block, and restores the previous one, if any, only upon
leaving the block.
The (default) :stdout and :stderr handlers will not trap output from
system() calls.
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(3)
