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Test::Tutorial

Section: Perl Programmers Reference Guide (3pm)
Updated: 2014-10-30
Index

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 writingdocumentation and having your fingernails pulled out? Did you open upa 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 foryou. 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 totesting. Your basic unit of testing is the ok. For each thing youtest, an "ok" is printed. Simple. Test::Harness interprets your testresults 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 );

and that does the same thing as the code above. "ok()" is the backboneof Perl testing, and we'll be using it instead of roll-your-own fromhere on. If "ok()" gets a true value, the test passes. False, itfails.

    #!/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 ensureyour test program ran all the way through and didn't die or skip sometests. "ok 1" ``The first test passed.'' "not ok 2" ``The second testfailed''. Test::Simple helpfully prints out some extra commentary aboutyour tests.

It's not scary. Come, hold my hand. We're going to give an exampleof testing a module. For our example, we'll be testing a datelibrary, Date::ICal. It's on CPAN, so download a copy and followalong. [2]

Where to start?

This is the hardest part of testing, where do you start? People oftenget overwhelmed at the apparent enormity of the task of testing awhole module. Best place to start is at the beginning. Date::ICal isan object-oriented module, and that means you start by making anobject. 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

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 twotests 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 secondargument 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 whatthe 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 linethe 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 thetest in the debugger or throw in some print statements to find out.

Instead, we'll switch from Test::Simple to Test::More. Test::Moredoes everything Test::Simple does, and more! In fact, Test::More doesthings exactly the way Test::Simple does. You can literally swapTest::Simple out and put Test::More in its place. That's just whatwe're going to do.

Test::More does more than Test::Simple. The most important differenceat this point is it provides more informative ways to say ``ok''.Although you can write almost any test with a generic "ok()", itcan't tell you what went wrong. Instead, we'll use the "is()"function, which lets us declare that something is supposed to be thesame as something else:

    #!/usr/bin/perl -w

    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 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. Aquick check shows that the code is working fine, we made a mistakewhen 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 youcan 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 arecode. Ergo, tests have bugs. A failing test could mean a bug in thecode, but don't discount the possibility that the test is wrong.

On the flip side, don't be tempted to prematurely declare a testincorrect just because you're having trouble finding the bug.Invalidating a test isn't something to be taken lightly, and don't useit 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 trickthe 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'llbe inclined to just throw more in as you think of them.Only problem is, every time we add to that we have to keep adjustingthe "use Test::More tests => ##" line. That can rapidly getannoying. There's two 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;

Or to be even more flexible, we use "no_plan". This means we're justrunning 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 tofigure 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 stringitself 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 thatwill make tracking down the problem easier. So try to put a bit ofdebugging information into the test names.

Describe what the tests test, to make debugging a failed test easierfor you or for the next person who runs your test.

Skipping tests

Poking around in the existing Date::ICal tests, I found this int/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 operatingsystems [8]. Even though Perl smooths out the differences for the mostpart, certain ports do it differently. MacPerl is one off the top ofmy head. [9] We know this will never work on MacOS. So rather thanjust putting a comment in the test, we can explicitly say it's nevergoing 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" );

        is( $t2->epoch, 0,          "  and back to ICal" );    }

A little bit of magic happens here. When running on anything butMacOS, all the tests run normally. But when on MacOS, "skip()" causesthe entire contents of the SKIP block to be jumped over. It's neverrun. Instead, it prints special output that tells Test::Harness thatthe 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 emailsfrom MacPerl users telling you about failing tests that you know willnever work. You've got to be careful with skip tests. These are fortests which don't work and never will. It is not for skippinggenuine 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 setthe date in the Date::ICal test suite. So I'll write 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 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 havethe time to fix this. [11] Normally, you'd just comment out the testand put a note in a todo list somewhere. Instead, we're going toexplicitly 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 afailure as a successful test. So you can write tests even beforeyou've fixed the underlying code.

If a TODO test passes, Test::Harness will report it ``UNEXPECTEDLYSUCCEEDED''. When that happens, you simply 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 globalfeatures. Once you turn it on, it affects all code in your programand all modules used (and all the modules they use). If a singlepiece of code isn't taint clean, the whole thing explodes. With thatin mind, it's very important to ensure your module works under taintmode.

It's very simple to have your tests run under taint mode. Just throwa "-T" into the "#!" line. Test::Harness will read the switchesin "#!" 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 andwarnings 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 hassome bugs, which is good --- we'll uncover them with our tests.
3: You can actually take this one step further and test the manualitself. 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 wedidn't say how many tests we're going to run, how can we know itfailed? No problem, Test::More employs some magic to catch that deathand turn the test into a failure, even if every test passed up to thatpoint.
7: I cleaned it up a little.
8: Most Operating Systems record time as the number of seconds since acertain date. This date is the beginning of the epoch. Unix's startsat 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 aproblem.
10: As long as the code inside the SKIP block at least compiles. Pleasedon't ask how. No, it's not a filter.
11: Do NOT be tempted to use TODO tests as a way to avoid fixing simplebugs!

AUTHORS

Michael G Schwern <schwernAATTpobox.com> and the perl-qa dancers!

COPYRIGHT

This documentation is free; you can redistribute it and/or modify itunder the same terms as Perl itself.

Irrespective of its distribution, all code examples in these filesare hereby placed into the public domain. You are permitted andencouraged to use this code in your own programs for funor for profit as you see fit. A simple comment in the code givingcredit would be courteous but is not required.

This document was created byman2html,using the manual pages.