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Test::Tutorial(3)      Perl Programmers	Reference Guide	     Test::Tutorial(3)

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@pobox.com> and the perl-qa dancers!

MAINTAINERS
       Chad Granum <exodist@cpan.org>

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 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 v5.28.3			  2020-05-14		     Test::Tutorial(3)

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