Provided by: libtest-differences-perl_0.69-1_all 
NAME
Test::Differences - Test strings and data structures and show differences if not ok
SYNOPSIS
use Test; ## Or use Test::More
use Test::Differences;
eq_or_diff $got, "a\nb\nc\n", "testing strings";
eq_or_diff \@got, [qw( a b c )], "testing arrays";
## Passing options:
eq_or_diff $got, $expected, $name, { context => 300 }; ## options
## Using with DBI-like data structures
use DBI;
... open connection & prepare statement and @expected_... here...
eq_or_diff $sth->fetchall_arrayref, \@expected_arrays "testing DBI arrays";
eq_or_diff $sth->fetchall_hashref, \@expected_hashes, "testing DBI hashes";
## To force textual or data line numbering (text lines are numbered 1..):
eq_or_diff_text ...;
eq_or_diff_data ...;
EXPORT
This module exports three test functions and four diff-style functions:
• Test functions
• "eq_or_diff"
• "eq_or_diff_data"
• "eq_or_diff_text"
• Diff style functions
• "table_diff" (the default)
• "unified_diff"
• "oldstyle_diff"
• "context_diff"
DESCRIPTION
When the code you're testing returns multiple lines, records or data structures and
they're just plain wrong, an equivalent to the Unix "diff" utility may be just what's
needed. Here's output from an example test script that checks two text documents and then
two (trivial) data structures:
t/99example....1..3
not ok 1 - differences in text
# Failed test ((eval 2) at line 14)
# +---+----------------+----------------+
# | Ln|Got |Expected |
# +---+----------------+----------------+
# | 1|this is line 1 |this is line 1 |
# * 2|this is line 2 |this is line b *
# | 3|this is line 3 |this is line 3 |
# +---+----------------+----------------+
not ok 2 - differences in whitespace
# Failed test ((eval 2) at line 20)
# +---+------------------+------------------+
# | Ln|Got |Expected |
# +---+------------------+------------------+
# | 1| indented | indented |
# * 2| indented |\tindented *
# | 3| indented | indented |
# +---+------------------+------------------+
not ok 3
# Failed test ((eval 2) at line 22)
# +----+-------------------------------------+----------------------------+
# | Elt|Got |Expected |
# +----+-------------------------------------+----------------------------+
# * 0|bless( [ |[ *
# * 1| 'Move along, nothing to see here' | 'Dry, humorless message' *
# * 2|], 'Test::Builder' ) |] *
# +----+-------------------------------------+----------------------------+
# Looks like you failed 3 tests of 3.
eq_or_diff_...() compares two strings or (limited) data structures and either emits an ok
indication or a side-by-side diff. Test::Differences is designed to be used with Test.pm
and with Test::Simple, Test::More, and other Test::Builder based testing modules. As the
SYNOPSIS shows, another testing module must be used as the basis for your test suite.
OPTIONS
The options to "eq_or_diff" give some fine-grained control over the output.
• "context"
This allows you to control the amount of context shown:
eq_or_diff $got, $expected, $name, { context => 50000 };
will show you lots and lots of context. Normally, eq_or_diff() uses some heuristics
to determine whether to show 3 lines of context (like a normal unified diff) or 25
lines.
• "data_type"
"text" or "data". This normally defaults to "data". If, however, neither of $got or
$expected is a reference then it defaults to "text". You can also force one or the
other by calling "eq_or_diff_text" or "eq_or_diff_data".
The difference is that in text mode lines are numbered from 1, but in data mode from 0
(and are refered to as 'elements' (Elt) instead of lines):
# +---+-------+----------+
# | Ln|Got |Expected |
# +---+-------+----------+
# * 1|'foo' |'bar' *
# +---+-------+----------+
# +----+---------+----+----------+
# | Elt|Got | Elt|Expected |
# +----+---------+----+----------+
# * 0|[ * 0|'bar' *
# * 1| 'foo' * | |
# * 2|] * | |
# +----+---------+----+----------+
The difference is purely cosmetic, it makes no difference to how comparisons are
performed.
• "Sortkeys"
If passed, whatever value is added is used as the argument for Data::Dumper Sortkeys
option. See the Data::Dumper docs to understand how you can control the Sortkeys
behavior.
• "filename_a" and "filename_b"
The column headers to use in the output. They default to 'Got' and 'Expected'.
DIFF STYLES
For extremely long strings, a table diff can wrap on your screen and be hard to read. If
you are comfortable with different diff formats, you can switch to a format more suitable
for your data. These are the four formats supported by the Text::Diff module and are set
with the following functions:
• "table_diff" (the default)
• "unified_diff"
• "oldstyle_diff"
• "context_diff"
You can run the following to understand the different diff output styles:
use Test::More 'no_plan';
use Test::Differences;
my $long_string = join '' => 1..40;
TODO: {
local $TODO = 'Testing diff styles';
# this is the default and does not need to explicitly set unless you need
# to reset it back from another diff type
table_diff;
eq_or_diff $long_string, "-$long_string", 'table diff';
unified_diff;
eq_or_diff $long_string, "-$long_string", 'unified diff';
context_diff;
eq_or_diff $long_string, "-$long_string", 'context diff';
oldstyle_diff;
eq_or_diff $long_string, "-$long_string", 'oldstyle diff';
}
UNICODE
Generally you'll find that the following test output is disappointing.
use Test::Differences;
use utf8;
my $want = { 'Traditional Chinese' => '中國' };
my $have = { 'Traditional Chinese' => '中国' };
eq_or_diff $have, $want, 'Unicode, baby';
Here's what you get:
# Failed test 'Unicode, baby'
# at t/unicode.t line 12.
# +----+-----------------------+-----------------------+
# | Elt|Got |Expected |
# +----+-----------------------+-----------------------+
# | 0|'Traditional Chinese' |'Traditional Chinese' |
# * 1|'\x{4e2d}\x{56fd}' |'\x{4e2d}\x{570b}' *
# +----+-----------------------+-----------------------+
# Looks like you failed 1 test of 1.
Dubious, test returned 1 (wstat 256, 0x100)
Failed 1/1 subtests
A patch to fix this would be *most* welcome.
Unknown::Values
Unknown::Values is a module which provides values which will never compare as being the
same as anything else, not even the same as itself.
If code looks too hard at one of these values (and Test::Differences looks very hard
indeed) that is a fatal error. This means that while we can detect the presence of these
beasties, and tell you that they compare different, for Complicated Internals Reasons we
can't show you much context. Sorry.
NB that the support for these is experimental and relies on an undocumented unstable
interface in Unknown::Values. If that fails then Test::Differences will probably just die
when it sees them instead of telling you that the comparison failed.
LIMITATIONS
"Test" or "Test::More"
This module "mixes in" with Test.pm or any of the test libraries based on Test::Builder
(Test::Simple, Test::More, etc). It does this by peeking to see whether Test.pm or
Test/Builder.pm is in %INC, so if you are not using one of those, it will print a warning
and play dumb by not emitting test numbers (or incrementing them). If you are using one
of these, it should interoperate nicely.
Exporting
Exports all 3 functions by default (and by design). Use
use Test::Differences ();
to suppress this behavior if you don't like the namespace pollution.
This module will not override functions like ok(), is(), is_deeply(), etc. If it did,
then you could "eval "use Test::Differences qw( is_deeply );"" to get automatic upgrading
to diffing behaviors without the "sub my_ok" shown above. Test::Differences intentionally
does not provide this behavior because this would mean that Test::Differences would need
to emulate every popular test module out there, which would require far more coding and
maintenance that I'm willing to do. Use the eval and my_ok deployment shown above if you
want some level of automation.
Unicode
Perls before 5.6.0 don't support characters > 255 at all, and 5.6.0 seems broken. This
means that you might get odd results using perl5.6.0 with unicode strings.
"Data::Dumper" and older Perls.
Relies on Data::Dumper (for now), which, prior to perl5.8, will not always report hashes
in the same order. $Data::Dumper::Sortkeys is set to 1, so on more recent versions of
Data::Dumper, this should not occur. Check CPAN to see if it's been peeled out of the
main perl distribution and backported. Reported by Ilya Martynov <ilya@martynov.org>,
although the Sortkeys "future perfect" workaround has been set in anticipation of a new
Data::Dumper for a while. Note that the two hashes should report the same here:
not ok 5
# Failed test (t/ctrl/05-home.t at line 51)
# +----+------------------------+----+------------------------+
# | Elt|Got | Elt|Expected |
# +----+------------------------+----+------------------------+
# | 0|{ | 0|{ |
# | 1| 'password' => '', | 1| 'password' => '', |
# * 2| 'method' => 'login', * | |
# | 3| 'ctrl' => 'home', | 2| 'ctrl' => 'home', |
# | | * 3| 'method' => 'login', *
# | 4| 'email' => 'test' | 4| 'email' => 'test' |
# | 5|} | 5|} |
# +----+------------------------+----+------------------------+
Data::Dumper also overlooks the difference between
$a[0] = \$a[1];
$a[1] = \$a[0]; # $a[0] = \$a[1]
and
$x = \$y;
$y = \$x;
@a = ( $x, $y ); # $a[0] = \$y, not \$a[1]
The former involves two scalars, the latter 4: $x, $y, and @a[0,1]. This was carefully
explained to me in words of two syllables or less by Yves Orton <demerphq@hotmail.com>.
The plan to address this is to allow you to select Data::Denter or some other module of
your choice as an option.
Code-refs
Test::Differences turns on $Data::Dumper::Deparse, so any code-refs in your data
structures will be turned into text before they are examined, using B::Deparse. The
precise text generated for a sub-ref might not be what you expect as it is generated from
the compiled version of the code, but it should at least be consistent and spot
differences correctly.
You can turn this behaviour off by setting $Test::Differences::NoDeparse.
AUTHORS
Barrie Slaymaker <barries@slaysys.com> - original author
Curtis "Ovid" Poe <ovid@cpan.org>
David Cantrell <david@cantrell.org.uk>
LICENSE
Copyright Barrie Slaymaker, Curtis "Ovid" Poe, and David Cantrell.
All Rights Reserved.
You may use, distribute and modify this software under the terms of the GNU public
license, any version, or the Artistic license.