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Test::Tutorial(3pPerl Programmers Reference GuiTest::Tutorial(3p)


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";

       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::Sim-
       ple 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.  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

       run that and you should get:




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           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 some-
       thing 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:




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           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 occured, 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::Sim-
       ple 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 impor-
       tant difference at this point is it provides more informa-
       tive 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
       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



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           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 ele-
       ments 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
       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 find-
       ing 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;



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           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.

       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



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       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]

           #!/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" );



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           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 differ-
       ently.  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" );

               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 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
       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



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       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.

           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';



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               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 underly-
       ing 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.

       Testing with taint mode.

       Taint mode is a funny thing.  It's the globalest of all
       global features.  Once you turn it on it effects 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

           use Test::More 'no_plan';

           ...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.




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       3   You can actually take this one step further and test
           the manual itself.  Have a look at Test::Inline (for-
           merly 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
           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 fil-
           ter.

       11  Do NOT be tempted to use TODO tests as a way to avoid
           fixing simple bugs!

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

COPYRIGHT
       Copyright 2001 by Michael G Schwern <schwernATpobox.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.







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