3 Test::Tutorial - A tutorial about writing really basic tests
8 I<AHHHHHHH!!!! NOT TESTING! Anything but testing!
9 Beat me, whip me, send me to Detroit, but don't make
14 I<Besides, I don't know how to write the damned things.>
17 Is this you? Is writing tests right up there with writing
18 documentation and having your fingernails pulled out? Did you open up
21 ######## We start with some black magic
23 and decide that's quite enough for you?
25 It's ok. That's all gone now. We've done all the black magic for
26 you. And here are the tricks...
29 =head2 Nuts and bolts of testing.
31 Here's the most basic test program.
37 print 1 + 1 == 2 ? "ok 1\n" : "not ok 1\n";
39 since 1 + 1 is 2, it prints:
44 What this says is: C<1..1> "I'm going to run one test." [1] C<ok 1>
45 "The first test passed". And that's about all magic there is to
46 testing. Your basic unit of testing is the I<ok>. For each thing you
47 test, an C<ok> is printed. Simple. B<Test::Harness> interprets your test
48 results to determine if you succeeded or failed (more on that later).
50 Writing all these print statements rapidly gets tedious. Fortunately,
51 there's B<Test::Simple>. It has one function, C<ok()>.
55 use Test::Simple tests => 1;
59 and that does the same thing as the code above. C<ok()> is the backbone
60 of Perl testing, and we'll be using it instead of roll-your-own from
61 here on. If C<ok()> gets a true value, the test passes. False, it
66 use Test::Simple tests => 2;
75 # Failed test (test.pl at line 5)
76 # Looks like you failed 1 tests of 2.
78 C<1..2> "I'm going to run two tests." This number is used to ensure
79 your test program ran all the way through and didn't die or skip some
80 tests. C<ok 1> "The first test passed." C<not ok 2> "The second test
81 failed". Test::Simple helpfully prints out some extra commentary about
84 It's not scary. Come, hold my hand. We're going to give an example
85 of testing a module. For our example, we'll be testing a date
86 library, B<Date::ICal>. It's on CPAN, so download a copy and follow
90 =head2 Where to start?
92 This is the hardest part of testing, where do you start? People often
93 get overwhelmed at the apparent enormity of the task of testing a
94 whole module. Best place to start is at the beginning. Date::ICal is
95 an object-oriented module, and that means you start by making an
96 object. So we test C<new()>.
100 use Test::Simple tests => 2;
104 my $ical = Date::ICal->new; # create an object
105 ok( defined $ical ); # check that we got something
106 ok( $ical->isa('Date::ICal') ); # and it's the right class
108 run that and you should get:
114 congratulations, you've written your first useful test.
119 That output isn't terribly descriptive, is it? When you have two
120 tests you can figure out which one is #2, but what if you have 102?
122 Each test can be given a little descriptive name as the second
125 use Test::Simple tests => 2;
127 ok( defined $ical, 'new() returned something' );
128 ok( $ical->isa('Date::ICal'), " and it's the right class" );
133 ok 1 - new() returned something
134 ok 2 - and it's the right class
137 =head2 Test the manual
139 Simplest way to build up a decent testing suite is to just test what
140 the manual says it does. [3] Let's pull something out of the
141 L<Date::ICal/SYNOPSIS> and test that all its bits work.
145 use Test::Simple tests => 8;
149 $ical = Date::ICal->new( year => 1964, month => 10, day => 16,
150 hour => 16, min => 12, sec => 47,
153 ok( defined $ical, 'new() returned something' );
154 ok( $ical->isa('Date::ICal'), " and it's the right class" );
155 ok( $ical->sec == 47, ' sec()' );
156 ok( $ical->min == 12, ' min()' );
157 ok( $ical->hour == 16, ' hour()' );
158 ok( $ical->day == 17, ' day()' );
159 ok( $ical->month == 10, ' month()' );
160 ok( $ical->year == 1964, ' year()' );
162 run that and you get:
165 ok 1 - new() returned something
166 ok 2 - and it's the right class
171 # Failed test (- at line 16)
174 # Looks like you failed 1 tests of 8.
176 Whoops, a failure! [4] Test::Simple helpfully lets us know on what line
177 the failure occured, but not much else. We were supposed to get 17,
178 but we didn't. What did we get?? Dunno. We'll have to re-run the
179 test in the debugger or throw in some print statements to find out.
181 Instead, we'll switch from B<Test::Simple> to B<Test::More>. B<Test::More>
182 does everything B<Test::Simple> does, and more! In fact, Test::More does
183 things I<exactly> the way Test::Simple does. You can literally swap
184 Test::Simple out and put Test::More in its place. That's just what
187 Test::More does more than Test::Simple. The most important difference
188 at this point is it provides more informative ways to say "ok".
189 Although you can write almost any test with a generic C<ok()>, it
190 can't tell you what went wrong. Instead, we'll use the C<is()>
191 function, which lets us declare that something is supposed to be the
192 same as something else:
196 use Test::More tests => 8;
200 $ical = Date::ICal->new( year => 1964, month => 10, day => 16,
201 hour => 16, min => 12, sec => 47,
204 ok( defined $ical, 'new() returned something' );
205 ok( $ical->isa('Date::ICal'), " and it's the right class" );
206 is( $ical->sec, 47, ' sec()' );
207 is( $ical->min, 12, ' min()' );
208 is( $ical->hour, 16, ' hour()' );
209 is( $ical->day, 17, ' day()' );
210 is( $ical->month, 10, ' month()' );
211 is( $ical->year, 1964, ' year()' );
213 "Is C<$ical-E<gt>sec> 47?" "Is C<$ical-E<gt>min> 12?" With C<is()> in place,
214 you get some more information
217 ok 1 - new() returned something
218 ok 2 - and it's the right class
223 # Failed test (- at line 16)
228 # Looks like you failed 1 tests of 8.
230 letting us know that C<$ical-E<gt>day> returned 16, but we expected 17. A
231 quick check shows that the code is working fine, we made a mistake
232 when writing up the tests. Just change it to:
234 is( $ical->day, 16, ' day()' );
236 and everything works.
238 So any time you're doing a "this equals that" sort of test, use C<is()>.
239 It even works on arrays. The test is always in scalar context, so you
240 can test how many elements are in a list this way. [5]
242 is( @foo, 5, 'foo has 5 elements' );
245 =head2 Sometimes the tests are wrong
247 Which brings us to a very important lesson. Code has bugs. Tests are
248 code. Ergo, tests have bugs. A failing test could mean a bug in the
249 code, but don't discount the possibility that the test is wrong.
251 On the flip side, don't be tempted to prematurely declare a test
252 incorrect just because you're having trouble finding the bug.
253 Invalidating a test isn't something to be taken lightly, and don't use
254 it as a cop out to avoid work.
257 =head2 Testing lots of values
259 We're going to be wanting to test a lot of dates here, trying to trick
260 the code with lots of different edge cases. Does it work before 1970?
261 After 2038? Before 1904? Do years after 10,000 give it trouble?
262 Does it get leap years right? We could keep repeating the code above,
263 or we could set up a little try/expect loop.
265 use Test::More tests => 32;
269 # An ICal string And the year, month, date
270 # hour, minute and second we expect.
271 '19971024T120000' => # from the docs.
272 [ 1997, 10, 24, 12, 0, 0 ],
273 '20390123T232832' => # after the Unix epoch
274 [ 2039, 1, 23, 23, 28, 32 ],
275 '19671225T000000' => # before the Unix epoch
276 [ 1967, 12, 25, 0, 0, 0 ],
277 '18990505T232323' => # before the MacOS epoch
278 [ 1899, 5, 5, 23, 23, 23 ],
282 while( my($ical_str, $expect) = each %ICal_Dates ) {
283 my $ical = Date::ICal->new( ical => $ical_str );
285 ok( defined $ical, "new(ical => '$ical_str')" );
286 ok( $ical->isa('Date::ICal'), " and it's the right class" );
288 is( $ical->year, $expect->[0], ' year()' );
289 is( $ical->month, $expect->[1], ' month()' );
290 is( $ical->day, $expect->[2], ' day()' );
291 is( $ical->hour, $expect->[3], ' hour()' );
292 is( $ical->min, $expect->[4], ' min()' );
293 is( $ical->sec, $expect->[5], ' sec()' );
296 So now we can test bunches of dates by just adding them to
297 C<%ICal_Dates>. Now that it's less work to test with more dates, you'll
298 be inclined to just throw more in as you think of them.
299 Only problem is, every time we add to that we have to keep adjusting
300 the C<use Test::More tests =E<gt> ##> line. That can rapidly get
301 annoying. Instead we use C<no_plan>. This means we're just running
302 some tests, don't know how many. [6]
304 use Test::More 'no_plan'; # instead of tests => 32
306 now we can just add tests and not have to do all sorts of math to
307 figure out how many we're running.
310 =head2 Informative names
312 Take a look at this line here
314 ok( defined $ical, "new(ical => '$ical_str')" );
316 we've added more detail about what we're testing and the ICal string
317 itself we're trying out to the name. So you get results like:
319 ok 25 - new(ical => '19971024T120000')
320 ok 26 - and it's the right class
328 if something in there fails, you'll know which one it was and that
329 will make tracking down the problem easier. So try to put a bit of
330 debugging information into the test names.
332 Describe what the tests test, to make debugging a failed test easier
333 for you or for the next person who runs your test.
336 =head2 Skipping tests
338 Poking around in the existing Date::ICal tests, I found this in
343 use Test::More tests => 7;
346 # Make sure epoch time is being handled sanely.
347 my $t1 = Date::ICal->new( epoch => 0 );
348 is( $t1->epoch, 0, "Epoch time of 0" );
350 # XXX This will only work on unix systems.
351 is( $t1->ical, '19700101Z', " epoch to ical" );
353 is( $t1->year, 1970, " year()" );
354 is( $t1->month, 1, " month()" );
355 is( $t1->day, 1, " day()" );
357 # like the tests above, but starting with ical instead of epoch
358 my $t2 = Date::ICal->new( ical => '19700101Z' );
359 is( $t2->ical, '19700101Z', "Start of epoch in ICal notation" );
361 is( $t2->epoch, 0, " and back to ICal" );
363 The beginning of the epoch is different on most non-Unix operating
364 systems [8]. Even though Perl smooths out the differences for the most
365 part, certain ports do it differently. MacPerl is one off the top of
366 my head. [9] We I<know> this will never work on MacOS. So rather than
367 just putting a comment in the test, we can explicitly say it's never
368 going to work and skip the test.
370 use Test::More tests => 7;
373 # Make sure epoch time is being handled sanely.
374 my $t1 = Date::ICal->new( epoch => 0 );
375 is( $t1->epoch, 0, "Epoch time of 0" );
378 skip('epoch to ICal not working on MacOS', 6)
381 is( $t1->ical, '19700101Z', " epoch to ical" );
383 is( $t1->year, 1970, " year()" );
384 is( $t1->month, 1, " month()" );
385 is( $t1->day, 1, " day()" );
387 # like the tests above, but starting with ical instead of epoch
388 my $t2 = Date::ICal->new( ical => '19700101Z' );
389 is( $t2->ical, '19700101Z', "Start of epoch in ICal notation" );
391 is( $t2->epoch, 0, " and back to ICal" );
394 A little bit of magic happens here. When running on anything but
395 MacOS, all the tests run normally. But when on MacOS, C<skip()> causes
396 the entire contents of the SKIP block to be jumped over. It's never
397 run. Instead, it prints special output that tells Test::Harness that
398 the tests have been skipped.
401 ok 1 - Epoch time of 0
402 ok 2 # skip epoch to ICal not working on MacOS
403 ok 3 # skip epoch to ICal not working on MacOS
404 ok 4 # skip epoch to ICal not working on MacOS
405 ok 5 # skip epoch to ICal not working on MacOS
406 ok 6 # skip epoch to ICal not working on MacOS
407 ok 7 # skip epoch to ICal not working on MacOS
409 This means your tests won't fail on MacOS. This means less emails
410 from MacPerl users telling you about failing tests that you know will
411 never work. You've got to be careful with skip tests. These are for
412 tests which don't work and I<never will>. It is not for skipping
413 genuine bugs (we'll get to that in a moment).
415 The tests are wholly and completely skipped. [10] This will work.
418 skip("I don't wanna die!");
420 die, die, die, die, die;
426 Thumbing through the Date::ICal man page, I came across this:
430 $ical_string = $ical->ical;
432 Retrieves, or sets, the date on the object, using any
433 valid ICal date/time string.
435 "Retrieves or sets". Hmmm, didn't see a test for using C<ical()> to set
436 the date in the Date::ICal test suite. So I'll write one.
438 use Test::More tests => 1;
440 my $ical = Date::ICal->new;
441 $ical->ical('20201231Z');
442 is( $ical->ical, '20201231Z', 'Setting via ical()' );
447 not ok 1 - Setting via ical()
448 # Failed test (- at line 6)
449 # got: '20010814T233649Z'
450 # expected: '20201231Z'
451 # Looks like you failed 1 tests of 1.
453 Whoops! Looks like it's unimplemented. Let's assume we don't have
454 the time to fix this. [11] Normally, you'd just comment out the test
455 and put a note in a todo list somewhere. Instead, we're going to
456 explicitly state "this test will fail" by wrapping it in a C<TODO> block.
458 use Test::More tests => 1;
461 local $TODO = 'ical($ical) not yet implemented';
463 my $ical = Date::ICal->new;
464 $ical->ical('20201231Z');
466 is( $ical->ical, '20201231Z', 'Setting via ical()' );
469 Now when you run, it's a little different:
472 not ok 1 - Setting via ical() # TODO ical($ical) not yet implemented
473 # got: '20010822T201551Z'
474 # expected: '20201231Z'
476 Test::More doesn't say "Looks like you failed 1 tests of 1". That '#
477 TODO' tells Test::Harness "this is supposed to fail" and it treats a
478 failure as a successful test. So you can write tests even before
479 you've fixed the underlying code.
481 If a TODO test passes, Test::Harness will report it "UNEXPECTEDLY
482 SUCCEEDED". When that happens, you simply remove the TODO block with
483 C<local $TODO> and turn it into a real test.
486 =head2 Testing with taint mode.
488 Taint mode is a funny thing. It's the globalest of all global
489 features. Once you turn it on it effects I<all> code in your program
490 and I<all> modules used (and all the modules they use). If a single
491 piece of code isn't taint clean, the whole thing explodes. With that
492 in mind, it's very important to ensure your module works under taint
495 It's very simple to have your tests run under taint mode. Just throw
496 a C<-T> into the C<#!> line. Test::Harness will read the switches
497 in C<#!> and use them to run your tests.
501 use Test::More 'no_plan';
503 ...test normally here...
505 So when you say C<make test> it will be run with taint mode and
515 The first number doesn't really mean anything, but it has to be 1.
516 It's the second number that's important.
520 For those following along at home, I'm using version 1.31. It has
521 some bugs, which is good -- we'll uncover them with our tests.
525 You can actually take this one step further and test the manual
526 itself. Have a look at B<Test::Inline> (formerly B<Pod::Tests>).
530 Yes, there's a mistake in the test suite. What! Me, contrived?
534 We'll get to testing the contents of lists later.
538 But what happens if your test program dies halfway through?! Since we
539 didn't say how many tests we're going to run, how can we know it
540 failed? No problem, Test::More employs some magic to catch that death
541 and turn the test into a failure, even if every test passed up to that
546 I cleaned it up a little.
550 Most Operating Systems record time as the number of seconds since a
551 certain date. This date is the beginning of the epoch. Unix's starts
552 at midnight January 1st, 1970 GMT.
556 MacOS's epoch is midnight January 1st, 1904. VMS's is midnight,
557 November 17th, 1858, but vmsperl emulates the Unix epoch so it's not a
562 As long as the code inside the SKIP block at least compiles. Please
563 don't ask how. No, it's not a filter.
567 Do NOT be tempted to use TODO tests as a way to avoid fixing simple
574 Michael G Schwern E<lt>schwern@pobox.comE<gt> and the perl-qa dancers!
578 Copyright 2001 by Michael G Schwern E<lt>schwern@pobox.comE<gt>.
580 This documentation is free; you can redistribute it and/or modify it
581 under the same terms as Perl itself.
583 Irrespective of its distribution, all code examples in these files
584 are hereby placed into the public domain. You are permitted and
585 encouraged to use this code in your own programs for fun
586 or for profit as you see fit. A simple comment in the code giving
587 credit would be courteous but is not required.