Test::Differences(3) User Contributed Perl Documentation Test::Differences(3)
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:
o Test functions
o "eq_or_diff"
o "eq_or_diff_data"
o "eq_or_diff_text"
o Diff style functions
o "table_diff" (the default)
o "unified_diff"
o "oldstyle_diff"
o "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.
o "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.
o "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.
o "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.
o "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:
o "table_diff" (the default)
o "unified_diff"
o "oldstyle_diff"
o "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;
my $want = { 'Traditional Chinese' => 'a,a' };
my $have = { 'Traditional Chinese' => 'a,a1/2' };
eq_or_diff $have, $want, 'Unicode, baby';
The output looks like this:
# Failed test 'Unicode, baby'
# at t/unicode.t line 12.
# +----+----------------------------+----------------------------+
# | Elt|Got |Expected |
# +----+----------------------------+----------------------------+
# | 0|'Traditional Chinese' |'Traditional Chinese' |
# * 1|'\xe4\xb8\xad\xe5\x9b\xbd' |'\xe4\xb8\xad\xe5\x9c\x8b' *
# +----+----------------------------+----------------------------+
# Looks like you failed 1 test of 1.
Dubious, test returned 1 (wstat 256, 0x100)
This is generally not helpful and someone points out that you didn't
declare your test program as being utf8, so you do that:
use Test::Differences;
use utf8;
my $want = { 'Traditional Chinese' => 'a,a' };
my $have = { 'Traditional Chinese' => 'a,a1/2' };
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
That's better, but still awful. However, if you have "Text::Diff" 0.40
or higher installed, you can add this to your code:
BEGIN { $ENV{DIFF_OUTPUT_UNICODE} = 1 }
Make sure you do this before you load Text::Diff. Then this is the
output:
# +----+-----------------------+-----------------------+
# | Elt|Got |Expected |
# +----+-----------------------+-----------------------+
# | 0|'Traditional Chinese' |'Traditional Chinese' |
# * 1|'a,a1/2' |'a,a' *
# +----+-----------------------+-----------------------+
DEPLOYING
There are several basic ways of deploying Test::Differences requiring
more or less labor by you or your users.
o Fallback to "is_deeply".
This is your best option if you want this module to be optional.
use Test::More;
BEGIN {
if (!eval q{ use Test::Differences; 1 }) {
*eq_or_diff = \&is_deeply;
}
}
o
eval "use Test::Differences";
If you want to detect the presence of Test::Differences on the fly,
something like the following code might do the trick for you:
use Test qw( !ok ); ## get all syms *except* ok
eval "use Test::Differences";
use Data::Dumper;
sub ok {
goto &eq_or_diff if defined &eq_or_diff && @_ > 1;
@_ = map ref $_ ? Dumper( @_ ) : $_, @_;
goto Test::&ok;
}
plan tests => 1;
ok "a", "b";
o PREREQ_PM => { .... "Test::Differences" => 0, ... }
This method will let CPAN and CPANPLUS users download it
automatically. It will discomfit those users who choose/have to
download all packages manually.
o t/lib/Test/Differences.pm, t/lib/Text/Diff.pm, ...
By placing Test::Differences and its prerequisites in the t/lib
directory, you avoid forcing your users to download the
Test::Differences manually if they aren't using CPAN or CPANPLUS.
If you put a "use lib "t/lib";" in the top of each test suite
before the "use Test::Differences;", "make test" should work well.
You might want to check once in a while for new Test::Differences
releases if you do this.
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.
perl v5.30.3 2021-05-18 Test::Differences(3)
test-differences 0680.0 - Generated Tue May 25 08:35:08 CDT 2021