Test(3pm) Perl Programmers Reference Guide Test(3pm)
NAME
Test - provides a simple framework for writing test scripts
SYNOPSIS
use strict;
use Test;
# use a BEGIN block so we print our plan before MyModule is loaded
BEGIN { plan tests => 14, todo => [3,4] }
# load your module...
use MyModule;
# Helpful notes. All note-lines must start with a "#".
print "# I'm testing MyModule version $MyModule::VERSION\n";
ok(0); # failure
ok(1); # success
ok(0); # ok, expected failure (see todo list, above)
ok(1); # surprise success!
ok(0,1); # failure: '0' ne '1'
ok('broke','fixed'); # failure: 'broke' ne 'fixed'
ok('fixed','fixed'); # success: 'fixed' eq 'fixed'
ok('fixed',qr/x/); # success: 'fixed' =~ qr/x/
ok(sub { 1+1 }, 2); # success: '2' eq '2'
ok(sub { 1+1 }, 3); # failure: '2' ne '3'
my @list = (0,0);
ok @list, 3, "\@list=".join(',',@list); #extra notes
ok 'segmentation fault', '/(?i)success/'; #regex match
skip(
$^O =~ m/MSWin/ ? "Skip if MSWin" : 0, # whether to skip
$foo, $bar # arguments just like for ok(...)
);
skip(
$^O =~ m/MSWin/ ? 0 : "Skip unless MSWin", # whether to skip
$foo, $bar # arguments just like for ok(...)
);
DESCRIPTION
This module simplifies the task of writing test files for Perl modules,
such that their output is in the format that Test::Harness expects to
see.
QUICK START GUIDE
To write a test for your new (and probably not even done) module,
create a new file called t/test.t (in a new t directory). If you have
multiple test files, to test the "foo", "bar", and "baz" feature sets,
then feel free to call your files t/foo.t, t/bar.t, and t/baz.t
Functions
This module defines three public functions, "plan(...)", "ok(...)", and
"skip(...)". By default, all three are exported by the "use Test;"
statement.
"plan(...)"
BEGIN { plan %theplan; }
This should be the first thing you call in your test script. It
declares your testing plan, how many there will be, if any of them
should be allowed to fail, and so on.
Typical usage is just:
use Test;
BEGIN { plan tests => 23 }
These are the things that you can put in the parameters to plan:
"tests => number"
The number of tests in your script. This means all ok() and
skip() calls.
"todo => [1,5,14]"
A reference to a list of tests which are allowed to fail. See
"TODO TESTS".
"onfail => sub { ... }"
"onfail => \&some_sub"
A subroutine reference to be run at the end of the test script,
if any of the tests fail. See "ONFAIL".
You must call "plan(...)" once and only once. You should call it
in a "BEGIN {...}" block, like so:
BEGIN { plan tests => 23 }
"ok(...)"
ok(1 + 1 == 2);
ok($have, $expect);
ok($have, $expect, $diagnostics);
This function is the reason for "Test"'s existence. It's the basic
function that handles printing ""ok"" or ""not ok"", along with the
current test number. (That's what "Test::Harness" wants to see.)
In its most basic usage, "ok(...)" simply takes a single scalar
expression. If its value is true, the test passes; if false, the
test fails. Examples:
# Examples of ok(scalar)
ok( 1 + 1 == 2 ); # ok if 1 + 1 == 2
ok( $foo =~ /bar/ ); # ok if $foo contains 'bar'
ok( baz($x + $y) eq 'Armondo' ); # ok if baz($x + $y) returns
# 'Armondo'
ok( @a == @b ); # ok if @a and @b are the same
# length
The expression is evaluated in scalar context. So the following
will work:
ok( @stuff ); # ok if @stuff has any
# elements
ok( !grep !defined $_, @stuff ); # ok if everything in @stuff
# is defined.
A special case is if the expression is a subroutine reference (in
either "sub {...}" syntax or "\&foo" syntax). In that case, it is
executed and its value (true or false) determines if the test
passes or fails. For example,
ok( sub { # See whether sleep works at least passably
my $start_time = time;
sleep 5;
time() - $start_time >= 4
});
In its two-argument form, "ok(arg1, arg2)" compares the two scalar
values to see if they match. They match if both are undefined, or
if arg2 is a regex that matches arg1, or if they compare equal with
"eq".
# Example of ok(scalar, scalar)
ok( "this", "that" ); # not ok, 'this' ne 'that'
ok( "", undef ); # not ok, "" is defined
The second argument is considered a regex if it is either a regex
object or a string that looks like a regex. Regex objects are
constructed with the qr// operator in recent versions of perl. A
string is considered to look like a regex if its first and last
characters are "/", or if the first character is "m" and its second
and last characters are both the same non-alphanumeric non-
whitespace character. These regexp
Regex examples:
ok( 'JaffO', '/Jaff/' ); # ok, 'JaffO' =~ /Jaff/
ok( 'JaffO', 'm|Jaff|' ); # ok, 'JaffO' =~ m|Jaff|
ok( 'JaffO', qr/Jaff/ ); # ok, 'JaffO' =~ qr/Jaff/;
ok( 'JaffO', '/(?i)jaff/ ); # ok, 'JaffO' =~ /jaff/i;
If either (or both!) is a subroutine reference, it is run and used
as the value for comparing. For example:
ok sub {
open(OUT, '>', 'x.dat') || die $!;
print OUT "\x{e000}";
close OUT;
my $bytecount = -s 'x.dat';
unlink 'x.dat' or warn "Can't unlink : $!";
return $bytecount;
},
4
;
The above test passes two values to "ok(arg1, arg2)" -- the first a
coderef, and the second is the number 4. Before "ok" compares
them, it calls the coderef, and uses its return value as the real
value of this parameter. Assuming that $bytecount returns 4, "ok"
ends up testing "4 eq 4". Since that's true, this test passes.
Finally, you can append an optional third argument, in
"ok(arg1,arg2, note)", where note is a string value that will be
printed if the test fails. This should be some useful information
about the test, pertaining to why it failed, and/or a description
of the test. For example:
ok( grep($_ eq 'something unique', @stuff), 1,
"Something that should be unique isn't!\n".
'@stuff = '.join ', ', @stuff
);
Unfortunately, a note cannot be used with the single argument style
of "ok()". That is, if you try "ok(arg1, note)", then "Test" will
interpret this as "ok(arg1, arg2)", and probably end up testing
"arg1 eq arg2" -- and that's not what you want!
All of the above special cases can occasionally cause some
problems. See "BUGS and CAVEATS".
"skip(skip_if_true, args...)"
This is used for tests that under some conditions can be skipped.
It's basically equivalent to:
if( $skip_if_true ) {
ok(1);
} else {
ok( args... );
}
...except that the ok(1) emits not just ""ok testnum"" but actually
""ok testnum # skip_if_true_value"".
The arguments after the skip_if_true are what is fed to "ok(...)"
if this test isn't skipped.
Example usage:
my $if_MSWin =
$^O =~ m/MSWin/ ? 'Skip if under MSWin' : '';
# A test to be skipped if under MSWin (i.e., run except under
# MSWin)
skip($if_MSWin, thing($foo), thing($bar) );
Or, going the other way:
my $unless_MSWin =
$^O =~ m/MSWin/ ? '' : 'Skip unless under MSWin';
# A test to be skipped unless under MSWin (i.e., run only under
# MSWin)
skip($unless_MSWin, thing($foo), thing($bar) );
The tricky thing to remember is that the first parameter is true if
you want to skip the test, not run it; and it also doubles as a
note about why it's being skipped. So in the first codeblock above,
read the code as "skip if MSWin -- (otherwise) test whether
"thing($foo)" is "thing($bar)"" or for the second case, "skip
unless MSWin...".
Also, when your skip_if_reason string is true, it really should
(for backwards compatibility with older Test.pm versions) start
with the string "Skip", as shown in the above examples.
Note that in the above cases, "thing($foo)" and "thing($bar)" are
evaluated -- but as long as the "skip_if_true" is true, then we
"skip(...)" just tosses out their value (i.e., not bothering to
treat them like values to "ok(...)". But if you need to not eval
the arguments when skipping the test, use this format:
skip( $unless_MSWin,
sub {
# This code returns true if the test passes.
# (But it doesn't even get called if the test is skipped.)
thing($foo) eq thing($bar)
}
);
or even this, which is basically equivalent:
skip( $unless_MSWin,
sub { thing($foo) }, sub { thing($bar) }
);
That is, both are like this:
if( $unless_MSWin ) {
ok(1); # but it actually appends "# $unless_MSWin"
# so that Test::Harness can tell it's a skip
} else {
# Not skipping, so actually call and evaluate...
ok( sub { thing($foo) }, sub { thing($bar) } );
}
TEST TYPES
o NORMAL TESTS
These tests are expected to succeed. Usually, most or all of your
tests are in this category. If a normal test doesn't succeed, then
that means that something is wrong.
o SKIPPED TESTS
The "skip(...)" function is for tests that might or might not be
possible to run, depending on the availability of platform-specific
features. The first argument should evaluate to true (think "yes,
please skip") if the required feature is not available. After the
first argument, "skip(...)" works exactly the same way as "ok(...)"
does.
o TODO TESTS
TODO tests are designed for maintaining an executable TODO list.
These tests are expected to fail. If a TODO test does succeed,
then the feature in question shouldn't be on the TODO list, now
should it?
Packages should NOT be released with succeeding TODO tests. As
soon as a TODO test starts working, it should be promoted to a
normal test, and the newly working feature should be documented in
the release notes or in the change log.
ONFAIL
BEGIN { plan test => 4, onfail => sub { warn "CALL 911!" } }
Although test failures should be enough, extra diagnostics can be
triggered at the end of a test run. "onfail" is passed an array ref of
hash refs that describe each test failure. Each hash will contain at
least the following fields: "package", "repetition", and "result".
(You shouldn't rely on any other fields being present.) If the test
had an expected value or a diagnostic (or "note") string, these will
also be included.
The optional "onfail" hook might be used simply to print out the
version of your package and/or how to report problems. It might also
be used to generate extremely sophisticated diagnostics for a
particularly bizarre test failure. However it's not a panacea. Core
dumps or other unrecoverable errors prevent the "onfail" hook from
running. (It is run inside an "END" block.) Besides, "onfail" is
probably over-kill in most cases. (Your test code should be simpler
than the code it is testing, yes?)
BUGS and CAVEATS
o "ok(...)"'s special handing of strings which look like they might
be regexes can also cause unexpected behavior. An innocent:
ok( $fileglob, '/path/to/some/*stuff/' );
will fail, since Test.pm considers the second argument to be a
regex! The best bet is to use the one-argument form:
ok( $fileglob eq '/path/to/some/*stuff/' );
o "ok(...)"'s use of string "eq" can sometimes cause odd problems
when comparing numbers, especially if you're casting a string to a
number:
$foo = "1.0";
ok( $foo, 1 ); # not ok, "1.0" ne 1
Your best bet is to use the single argument form:
ok( $foo == 1 ); # ok "1.0" == 1
o As you may have inferred from the above documentation and examples,
"ok"'s prototype is "($;$$)" (and, incidentally, "skip"'s is
"($;$$$)"). This means, for example, that you can do "ok @foo,
@bar" to compare the size of the two arrays. But don't be fooled
into thinking that "ok @foo, @bar" means a comparison of the
contents of two arrays -- you're comparing just the number of
elements of each. It's so easy to make that mistake in reading "ok
@foo, @bar" that you might want to be very explicit about it, and
instead write "ok scalar(@foo), scalar(@bar)".
o This almost definitely doesn't do what you expect:
ok $thingy->can('some_method');
Why? Because "can" returns a coderef to mean "yes it can (and the
method is this...)", and then "ok" sees a coderef and thinks you're
passing a function that you want it to call and consider the truth
of the result of! I.e., just like:
ok $thingy->can('some_method')->();
What you probably want instead is this:
ok $thingy->can('some_method') && 1;
If the "can" returns false, then that is passed to "ok". If it
returns true, then the larger expression
"$thingy->can('some_method') && 1" returns 1, which "ok" sees as a
simple signal of success, as you would expect.
o The syntax for "skip" is about the only way it can be, but it's
still quite confusing. Just start with the above examples and
you'll be okay.
Moreover, users may expect this:
skip $unless_mswin, foo($bar), baz($quux);
to not evaluate "foo($bar)" and "baz($quux)" when the test is being
skipped. But in reality, they are evaluated, but "skip" just won't
bother comparing them if $unless_mswin is true.
You could do this:
skip $unless_mswin, sub{foo($bar)}, sub{baz($quux)};
But that's not terribly pretty. You may find it simpler or clearer
in the long run to just do things like this:
if( $^O =~ m/MSWin/ ) {
print "# Yay, we're under $^O\n";
ok foo($bar), baz($quux);
ok thing($whatever), baz($stuff);
ok blorp($quux, $whatever);
ok foo($barzbarz), thang($quux);
} else {
print "# Feh, we're under $^O. Watch me skip some tests...\n";
for(1 .. 4) { skip "Skip unless under MSWin" }
}
But be quite sure that "ok" is called exactly as many times in the
first block as "skip" is called in the second block.
ENVIRONMENT
If "PERL_TEST_DIFF" environment variable is set, it will be used as a
command for comparing unexpected multiline results. If you have GNU
diff installed, you might want to set "PERL_TEST_DIFF" to "diff -u".
If you don't have a suitable program, you might install the
"Text::Diff" module and then set "PERL_TEST_DIFF" to be "perl
-MText::Diff -e 'print diff(@ARGV)'". If "PERL_TEST_DIFF" isn't set
but the "Algorithm::Diff" module is available, then it will be used to
show the differences in multiline results.
NOTE
A past developer of this module once said that it was no longer being
actively developed. However, rumors of its demise were greatly
exaggerated. Feedback and suggestions are quite welcome.
Be aware that the main value of this module is its simplicity. Note
that there are already more ambitious modules out there, such as
Test::More and Test::Unit.
Some earlier versions of this module had docs with some confusing typos
in the description of "skip(...)".
SEE ALSO
Test::Harness
Test::Simple, Test::More, Devel::Cover
Test::Builder for building your own testing library.
Test::Unit is an interesting XUnit-style testing library.
Test::Inline lets you embed tests in code.
AUTHOR
Copyright (c) 1998-2000 Joshua Nathaniel Pritikin.
Copyright (c) 2001-2002 Michael G. Schwern.
Copyright (c) 2002-2004 Sean M. Burke.
Current maintainer: Jesse Vincent. <jesse AT bestpractical.com>
This package is free software and is provided "as is" without express
or implied warranty. It may be used, redistributed and/or modified
under the same terms as Perl itself.
perl v5.26.3 2018-03-23 Test(3pm)
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