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Test::Tutorial(3perl) Perl Programmers Reference Guide Test::Tutorial(3perl)
NAME
Test::Tutorial - A tutorial about writing really basic tests
DESCRIPTION
AHHHHHHH!!!! NOT TESTING! Anything but testing! Beat me, whip me, send me to Detroit,
but don't make me write tests!
*sob*
Besides, I don't know how to write the damned things.
Is this you? Is writing tests right up there with writing documentation and having your
fingernails pulled out? Did you open up a test and read
######## We start with some black magic
and decide that's quite enough for you?
It's ok. That's all gone now. We've done all the black magic for you. And here are the
tricks...
Nuts and bolts of testing.
Here's the most basic test program.
#!/usr/bin/perl -w
print "1..1\n";
print 1 + 1 == 2 ? "ok 1\n" : "not ok 1\n";
Because 1 + 1 is 2, it prints:
1..1
ok 1
What this says is: 1..1 "I'm going to run one test." [1] "ok 1" "The first test passed".
And that's about all magic there is to testing. Your basic unit of testing is the ok.
For each thing you test, an "ok" is printed. Simple. Test::Harness interprets your test
results to determine if you succeeded or failed (more on that later).
Writing all these print statements rapidly gets tedious. Fortunately, there's
Test::Simple. It has one function, "ok()".
#!/usr/bin/perl -w
use Test::Simple tests => 1;
ok( 1 + 1 == 2 );
That does the same thing as the previous code. "ok()" is the backbone of Perl testing,
and we'll be using it instead of roll-your-own from here on. If "ok()" gets a true value,
the test passes. False, it fails.
#!/usr/bin/perl -w
use Test::Simple tests => 2;
ok( 1 + 1 == 2 );
ok( 2 + 2 == 5 );
From that comes:
1..2
ok 1
not ok 2
# Failed test (test.pl at line 5)
# Looks like you failed 1 tests of 2.
1..2 "I'm going to run two tests." This number is a plan. It helps to ensure your test
program ran all the way through and didn't die or skip some tests. "ok 1" "The first test
passed." "not ok 2" "The second test failed". Test::Simple helpfully prints out some
extra commentary about your tests.
It's not scary. Come, hold my hand. We're going to give an example of testing a module.
For our example, we'll be testing a date library, Date::ICal. It's on CPAN, so download a
copy and follow along. [2]
Where to start?
This is the hardest part of testing, where do you start? People often get overwhelmed at
the apparent enormity of the task of testing a whole module. The best place to start is
at the beginning. Date::ICal is an object-oriented module, and that means you start by
making an object. Test "new()".
#!/usr/bin/perl -w
# assume these two lines are in all subsequent examples
use strict;
use warnings;
use Test::Simple tests => 2;
use Date::ICal;
my $ical = Date::ICal->new; # create an object
ok( defined $ical ); # check that we got something
ok( $ical->isa('Date::ICal') ); # and it's the right class
Run that and you should get:
1..2
ok 1
ok 2
Congratulations! You've written your first useful test.
Names
That output isn't terribly descriptive, is it? When you have two tests you can figure out
which one is #2, but what if you have 102 tests?
Each test can be given a little descriptive name as the second argument to "ok()".
use Test::Simple tests => 2;
ok( defined $ical, 'new() returned something' );
ok( $ical->isa('Date::ICal'), " and it's the right class" );
Now you'll see:
1..2
ok 1 - new() returned something
ok 2 - and it's the right class
Test the manual
The simplest way to build up a decent testing suite is to just test what the manual says
it does. [3] Let's pull something out of the "SYNOPSIS" in Date::ICal and test that all
its bits work.
#!/usr/bin/perl -w
use Test::Simple tests => 8;
use Date::ICal;
$ical = Date::ICal->new( year => 1964, month => 10, day => 16,
hour => 16, min => 12, sec => 47,
tz => '0530' );
ok( defined $ical, 'new() returned something' );
ok( $ical->isa('Date::ICal'), " and it's the right class" );
ok( $ical->sec == 47, ' sec()' );
ok( $ical->min == 12, ' min()' );
ok( $ical->hour == 16, ' hour()' );
ok( $ical->day == 17, ' day()' );
ok( $ical->month == 10, ' month()' );
ok( $ical->year == 1964, ' year()' );
Run that and you get:
1..8
ok 1 - new() returned something
ok 2 - and it's the right class
ok 3 - sec()
ok 4 - min()
ok 5 - hour()
not ok 6 - day()
# Failed test (- at line 16)
ok 7 - month()
ok 8 - year()
# Looks like you failed 1 tests of 8.
Whoops, a failure! [4] Test::Simple helpfully lets us know on what line the failure
occurred, but not much else. We were supposed to get 17, but we didn't. What did we
get?? Dunno. You could re-run the test in the debugger or throw in some print statements
to find out.
Instead, switch from Test::Simple to Test::More. Test::More does everything Test::Simple
does, and more! In fact, Test::More does things exactly the way Test::Simple does. You
can literally swap Test::Simple out and put Test::More in its place. That's just what
we're going to do.
Test::More does more than Test::Simple. The most important difference at this point is it
provides more informative ways to say "ok". Although you can write almost any test with a
generic "ok()", it can't tell you what went wrong. The "is()" function lets us declare
that something is supposed to be the same as something else:
use Test::More tests => 8;
use Date::ICal;
$ical = Date::ICal->new( year => 1964, month => 10, day => 16,
hour => 16, min => 12, sec => 47,
tz => '0530' );
ok( defined $ical, 'new() returned something' );
ok( $ical->isa('Date::ICal'), " and it's the right class" );
is( $ical->sec, 47, ' sec()' );
is( $ical->min, 12, ' min()' );
is( $ical->hour, 16, ' hour()' );
is( $ical->day, 17, ' day()' );
is( $ical->month, 10, ' month()' );
is( $ical->year, 1964, ' year()' );
"Is "$ical->sec" 47?" "Is "$ical->min" 12?" With "is()" in place, you get more
information:
1..8
ok 1 - new() returned something
ok 2 - and it's the right class
ok 3 - sec()
ok 4 - min()
ok 5 - hour()
not ok 6 - day()
# Failed test (- at line 16)
# got: '16'
# expected: '17'
ok 7 - month()
ok 8 - year()
# Looks like you failed 1 tests of 8.
Aha. "$ical->day" returned 16, but we expected 17. A quick check shows that the code is
working fine, we made a mistake when writing the tests. Change it to:
is( $ical->day, 16, ' day()' );
... and everything works.
Any time you're doing a "this equals that" sort of test, use "is()". It even works on
arrays. The test is always in scalar context, so you can test how many elements are in an
array this way. [5]
is( @foo, 5, 'foo has 5 elements' );
Sometimes the tests are wrong
This brings up a very important lesson. Code has bugs. Tests are code. Ergo, tests have
bugs. A failing test could mean a bug in the code, but don't discount the possibility
that the test is wrong.
On the flip side, don't be tempted to prematurely declare a test incorrect just because
you're having trouble finding the bug. Invalidating a test isn't something to be taken
lightly, and don't use it as a cop out to avoid work.
Testing lots of values
We're going to be wanting to test a lot of dates here, trying to trick the code with lots
of different edge cases. Does it work before 1970? After 2038? Before 1904? Do years
after 10,000 give it trouble? Does it get leap years right? We could keep repeating the
code above, or we could set up a little try/expect loop.
use Test::More tests => 32;
use Date::ICal;
my %ICal_Dates = (
# An ICal string And the year, month, day
# hour, minute and second we expect.
'19971024T120000' => # from the docs.
[ 1997, 10, 24, 12, 0, 0 ],
'20390123T232832' => # after the Unix epoch
[ 2039, 1, 23, 23, 28, 32 ],
'19671225T000000' => # before the Unix epoch
[ 1967, 12, 25, 0, 0, 0 ],
'18990505T232323' => # before the MacOS epoch
[ 1899, 5, 5, 23, 23, 23 ],
);
while( my($ical_str, $expect) = each %ICal_Dates ) {
my $ical = Date::ICal->new( ical => $ical_str );
ok( defined $ical, "new(ical => '$ical_str')" );
ok( $ical->isa('Date::ICal'), " and it's the right class" );
is( $ical->year, $expect->[0], ' year()' );
is( $ical->month, $expect->[1], ' month()' );
is( $ical->day, $expect->[2], ' day()' );
is( $ical->hour, $expect->[3], ' hour()' );
is( $ical->min, $expect->[4], ' min()' );
is( $ical->sec, $expect->[5], ' sec()' );
}
Now we can test bunches of dates by just adding them to %ICal_Dates. Now that it's less
work to test with more dates, you'll be inclined to just throw more in as you think of
them. Only problem is, every time we add to that we have to keep adjusting the "use
Test::More tests => ##" line. That can rapidly get annoying. There are ways to make this
work better.
First, we can calculate the plan dynamically using the "plan()" function.
use Test::More;
use Date::ICal;
my %ICal_Dates = (
...same as before...
);
# For each key in the hash we're running 8 tests.
plan tests => keys(%ICal_Dates) * 8;
...and then your tests...
To be even more flexible, use "done_testing". This means we're just running some tests,
don't know how many. [6]
use Test::More; # instead of tests => 32
... # tests here
done_testing(); # reached the end safely
If you don't specify a plan, Test::More expects to see "done_testing()" before your
program exits. It will warn you if you forget it. You can give "done_testing()" an
optional number of tests you expected to run, and if the number ran differs, Test::More
will give you another kind of warning.
Informative names
Take a look at the line:
ok( defined $ical, "new(ical => '$ical_str')" );
We've added more detail about what we're testing and the ICal string itself we're trying
out to the name. So you get results like:
ok 25 - new(ical => '19971024T120000')
ok 26 - and it's the right class
ok 27 - year()
ok 28 - month()
ok 29 - day()
ok 30 - hour()
ok 31 - min()
ok 32 - sec()
If something in there fails, you'll know which one it was and that will make tracking down
the problem easier. Try to put a bit of debugging information into the test names.
Describe what the tests test, to make debugging a failed test easier for you or for the
next person who runs your test.
Skipping tests
Poking around in the existing Date::ICal tests, I found this in t/01sanity.t [7]
#!/usr/bin/perl -w
use Test::More tests => 7;
use Date::ICal;
# Make sure epoch time is being handled sanely.
my $t1 = Date::ICal->new( epoch => 0 );
is( $t1->epoch, 0, "Epoch time of 0" );
# XXX This will only work on unix systems.
is( $t1->ical, '19700101Z', " epoch to ical" );
is( $t1->year, 1970, " year()" );
is( $t1->month, 1, " month()" );
is( $t1->day, 1, " day()" );
# like the tests above, but starting with ical instead of epoch
my $t2 = Date::ICal->new( ical => '19700101Z' );
is( $t2->ical, '19700101Z', "Start of epoch in ICal notation" );
is( $t2->epoch, 0, " and back to ICal" );
The beginning of the epoch is different on most non-Unix operating systems [8]. Even
though Perl smooths out the differences for the most part, certain ports do it
differently. MacPerl is one off the top of my head. [9] Rather than putting a comment in
the test and hoping someone will read the test while debugging the failure, we can
explicitly say it's never going to work and skip the test.
use Test::More tests => 7;
use Date::ICal;
# Make sure epoch time is being handled sanely.
my $t1 = Date::ICal->new( epoch => 0 );
is( $t1->epoch, 0, "Epoch time of 0" );
SKIP: {
skip('epoch to ICal not working on Mac OS', 6)
if $^O eq 'MacOS';
is( $t1->ical, '19700101Z', " epoch to ical" );
is( $t1->year, 1970, " year()" );
is( $t1->month, 1, " month()" );
is( $t1->day, 1, " day()" );
# like the tests above, but starting with ical instead of epoch
my $t2 = Date::ICal->new( ical => '19700101Z' );
is( $t2->ical, '19700101Z', "Start of epoch in ICal notation" );
is( $t2->epoch, 0, " and back to ICal" );
}
A little bit of magic happens here. When running on anything but MacOS, all the tests run
normally. But when on MacOS, "skip()" causes the entire contents of the SKIP block to be
jumped over. It never runs. Instead, "skip()" prints special output that tells
Test::Harness that the tests have been skipped.
1..7
ok 1 - Epoch time of 0
ok 2 # skip epoch to ICal not working on MacOS
ok 3 # skip epoch to ICal not working on MacOS
ok 4 # skip epoch to ICal not working on MacOS
ok 5 # skip epoch to ICal not working on MacOS
ok 6 # skip epoch to ICal not working on MacOS
ok 7 # skip epoch to ICal not working on MacOS
This means your tests won't fail on MacOS. This means fewer emails from MacPerl users
telling you about failing tests that you know will never work. You've got to be careful
with skip tests. These are for tests which don't work and never will. It is not for
skipping genuine bugs (we'll get to that in a moment).
The tests are wholly and completely skipped. [10] This will work.
SKIP: {
skip("I don't wanna die!");
die, die, die, die, die;
}
Todo tests
While thumbing through the Date::ICal man page, I came across this:
ical
$ical_string = $ical->ical;
Retrieves, or sets, the date on the object, using any
valid ICal date/time string.
"Retrieves or sets". Hmmm. I didn't see a test for using "ical()" to set the date in the
Date::ICal test suite. So I wrote one:
use Test::More tests => 1;
use Date::ICal;
my $ical = Date::ICal->new;
$ical->ical('20201231Z');
is( $ical->ical, '20201231Z', 'Setting via ical()' );
Run that. I saw:
1..1
not ok 1 - Setting via ical()
# Failed test (- at line 6)
# got: '20010814T233649Z'
# expected: '20201231Z'
# Looks like you failed 1 tests of 1.
Whoops! Looks like it's unimplemented. Assume you don't have the time to fix this. [11]
Normally, you'd just comment out the test and put a note in a todo list somewhere.
Instead, explicitly state "this test will fail" by wrapping it in a "TODO" block:
use Test::More tests => 1;
TODO: {
local $TODO = 'ical($ical) not yet implemented';
my $ical = Date::ICal->new;
$ical->ical('20201231Z');
is( $ical->ical, '20201231Z', 'Setting via ical()' );
}
Now when you run, it's a little different:
1..1
not ok 1 - Setting via ical() # TODO ical($ical) not yet implemented
# got: '20010822T201551Z'
# expected: '20201231Z'
Test::More doesn't say "Looks like you failed 1 tests of 1". That '# TODO' tells
Test::Harness "this is supposed to fail" and it treats a failure as a successful test.
You can write tests even before you've fixed the underlying code.
If a TODO test passes, Test::Harness will report it "UNEXPECTEDLY SUCCEEDED". When that
happens, remove the TODO block with "local $TODO" and turn it into a real test.
Testing with taint mode.
Taint mode is a funny thing. It's the globalest of all global features. Once you turn it
on, it affects all code in your program and all modules used (and all the modules they
use). If a single piece of code isn't taint clean, the whole thing explodes. With that
in mind, it's very important to ensure your module works under taint mode.
It's very simple to have your tests run under taint mode. Just throw a "-T" into the "#!"
line. Test::Harness will read the switches in "#!" and use them to run your tests.
#!/usr/bin/perl -Tw
...test normally here...
When you say "make test" it will run with taint mode on.
FOOTNOTES
1. The first number doesn't really mean anything, but it has to be 1. It's the second
number that's important.
2. For those following along at home, I'm using version 1.31. It has some bugs, which is
good -- we'll uncover them with our tests.
3. You can actually take this one step further and test the manual itself. Have a look
at Test::Inline (formerly Pod::Tests).
4. Yes, there's a mistake in the test suite. What! Me, contrived?
5. We'll get to testing the contents of lists later.
6. But what happens if your test program dies halfway through?! Since we didn't say how
many tests we're going to run, how can we know it failed? No problem, Test::More
employs some magic to catch that death and turn the test into a failure, even if every
test passed up to that point.
7. I cleaned it up a little.
8. Most Operating Systems record time as the number of seconds since a certain date.
This date is the beginning of the epoch. Unix's starts at midnight January 1st, 1970
GMT.
9. MacOS's epoch is midnight January 1st, 1904. VMS's is midnight, November 17th, 1858,
but vmsperl emulates the Unix epoch so it's not a problem.
10. As long as the code inside the SKIP block at least compiles. Please don't ask how.
No, it's not a filter.
11. Do NOT be tempted to use TODO tests as a way to avoid fixing simple bugs!
AUTHORS
Michael G Schwern <schwern AT pobox.com> and the perl-qa dancers!
MAINTAINERS
Chad Granum <exodist AT cpan.org>
COPYRIGHT
Copyright 2001 by Michael G Schwern <schwern AT pobox.com>.
This documentation is free; you can redistribute it and/or modify it under the same terms
as Perl itself.
Irrespective of its distribution, all code examples in these files are hereby placed into
the public domain. You are permitted and encouraged to use this code in your own programs
for fun or for profit as you see fit. A simple comment in the code giving credit would be
courteous but is not required.
perl v5.30.0 2023-11-23 Test::Tutorial(3perl)
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On Apache
Under GNU General Public License
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