Test::Tutorial(3pPerl Programmers Reference GuiTest::Tutorial(3p)NAMETest::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";
since 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;
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ok( 1 + 1 == 2 );
and that does the same thing as the code above. "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 used 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 down-
load 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. Best place to start is at
the beginning. Date::ICal is an object-oriented module, and
that means you start by making an object. So we test
"new()".
#!/usr/bin/perl -w
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
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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?
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" );
So now you'd see...
1..2
ok 1 - new() returned something
ok 2 - and it's the right class
Test the manual
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' );
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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( $ical->year == 1964, ' year()' );
run that and you get:
1..8
ok 1 - new() returned something
ok 2 - and it's the right class
ok 3 - sec()
ok 4 - min()
ok 5 - hour()
not ok 6 - day()
# Failed test (- at line 16)
ok 7 - month()
ok 8 - year()
# Looks like you failed 1 tests of 8.
Whoops, a failure! [4] Test::Simple helpfully lets us know
on what line the failure occurred, but not much else. We
were supposed to get 17, but we didn't. What did we get??
Dunno. We'll have to re-run the test in the debugger or
throw in some print statements to find out.
Instead, we'll switch from Test::Simple to Test::More.
Test::More does everything Test::Simple does, and more! In
fact, Test::More does things exactly the way Test::Simple
does. You can literally swap Test::Simple out and put
Test::More in its place. That's just what we're going to
do.
Test::More does more than Test::Simple. The most important
difference at this point is it provides more informative
ways to say "ok". Although you can write almost any test
with a generic "ok()", it can't tell you what went wrong.
Instead, we'll use the "is()" function, which lets us
declare that something is supposed to be the same as some-
thing else:
#!/usr/bin/perl -w
use Test::More tests => 8;
use Date::ICal;
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$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 "$ical->min" 12?" With "is()" in
place, you get some more information
1..8
ok 1 - new() returned something
ok 2 - and it's the right class
ok 3 - sec()
ok 4 - min()
ok 5 - hour()
not ok 6 - day()
# Failed test (- at line 16)
# got: '16'
# expected: '17'
ok 7 - month()
ok 8 - year()
# Looks like you failed 1 tests of 8.
letting us know that "$ical->day" returned 16, but we
expected 17. A quick check shows that the code is working
fine, we made a mistake when writing up the tests. Just
change it to:
is( $ical->day, 16, ' day()' );
and everything works.
So any time you're doing a "this equals that" sort of test,
use "is()". It even works on arrays. The test is always in
scalar context, so you can test how many elements are in a
list this way. [5]
is( @foo, 5, 'foo has 5 elements' );
Sometimes the tests are wrong
Which brings us to a very important lesson. Code has bugs.
Tests are code. Ergo, tests have bugs. A failing test
could mean a bug in the code, but don't discount the possi-
bility that the test is wrong.
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On the flip side, don't be tempted to prematurely declare a
test incorrect just because you're having trouble finding
the bug. Invalidating a test isn't something to be taken
lightly, and don't use it as a cop out to avoid work.
Testing lots of values
We're going to be wanting to test a lot of dates here, try-
ing to trick the code with lots of different edge cases.
Does it work before 1970? After 2038? Before 1904? Do
years after 10,000 give it trouble? Does it get leap years
right? We could keep repeating the code above, or we could
set up a little try/expect loop.
use Test::More tests => 32;
use Date::ICal;
my %ICal_Dates = (
# An ICal string And the year, month, date
# hour, minute and second we expect.
'19971024T120000' => # from the docs.
[ 1997, 10, 24, 12, 0, 0 ],
'20390123T232832' => # after the Unix epoch
[ 2039, 1, 23, 23, 28, 32 ],
'19671225T000000' => # before the Unix epoch
[ 1967, 12, 25, 0, 0, 0 ],
'18990505T232323' => # before the MacOS epoch
[ 1899, 5, 5, 23, 23, 23 ],
);
while( my($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()' );
}
So 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's two ways to make
this work better.
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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;
Or to be even more flexible, we use "no_plan". This means
we're just running some tests, don't know how many. [6]
use Test::More 'no_plan'; # instead of tests => 32
now we can just add tests and not have to do all sorts of
math to figure out how many we're running.
Informative names
Take a look at this line here
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. So 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]
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#!/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 dif-
ferently. MacPerl is one off the top of my head. [9] We
know this will never work on MacOS. So rather than just
putting a comment in the test, 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 MacOS', 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" );
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is( $t2->epoch, 0, " and back to ICal" );
}
A little bit of magic happens here. When running on any-
thing 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's never run. Instead, it prints spe-
cial 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 less
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
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, didn't see a test for using
"ical()" to set the date in the Date::ICal test suite. So
I'll write one.
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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 and I get
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. Let's assume we
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 some-
where. Instead, we're going to 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. So you can
write tests even before you've fixed the underlying code.
If a TODO test passes, Test::Harness will report it "UNEX-
PECTEDLY SUCCEEDED". When that happens, you simply remove
the TODO block with "local $TODO" and turn it into a real
test.
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Testing with taint mode.
Taint mode is a funny thing. It's the globalest of all glo-
bal 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 impor-
tant 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...
So when you say "make test" it will be run with taint mode
and warnings 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 begin-
ning of the epoch. Unix's starts at midnight January
1st, 1970 GMT.
9 MacOS's epoch is midnight January 1st, 1904. VMS's is
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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 com-
piles. 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@pobox.com> and the perl-qa danc-
ers!
COPYRIGHT
Copyright 2001 by Michael G Schwern <schwern@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 pro-
grams for fun or for profit as you see fit. A simple com-
ment in the code giving credit would be courteous but is not
required.
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