Let’s assume for the moment that you’re writ­ing a Perl mod­ule or appli­ca­tion. You’d like to main­tain some lev­el of soft­ware qual­i­ty (or kwali­tee), so you’re writ­ing a suite of test scripts. Whether you’re writ­ing them first (good for you for prac­tic­ing test-​driven devel­op­ment!) or the appli­ca­tion code is already there, you’ll prob­a­bly be reach­ing for Test::Simple, Test::More, or one of the Test2::Suite bun­dles. With the lat­ter two you’re imme­di­ate­ly con­front­ed with a choice: do you count up the num­ber of tests into a plan, or do you for­sake that in favor of leav­ing a done_testing() call at the end of your test script(s)?

There are good argu­ments for both approach­es. When you first start, you prob­a­bly have no idea how many tests your scripts will con­tain. After all, a test script can be a use­ful tool for design­ing a mod­ule’s inter­face by writ­ing exam­ple code that will use it. Your explorato­ry code would be writ­ten as if the mod­ule or appli­ca­tion was already done, test­ing it in the way you’d like it to work. Not declar­ing a plan makes per­fect sense in this case; just put done_testing() at the end and get back to defin­ing your tests.

You don’t have that option when using Test::Simple, of course—it’s so basic it only has one func­tion (ok()), and you have to pre-​declare how many tests you plan to run when useing the mod­ule, like so:

use Test::Simple tests => 23;

Test::More also sup­ports this form of plan, or you can opt to use its plan func­tion to state the num­ber of tests in your script or subtest. With Test2 you have to use plan. Either way, the plan acts as a sort of meta-​test, mak­ing sure that you exe­cut­ed exact­ly what you intend­ed: no more, no less. While there are sit­u­a­tions where it’s not pos­si­ble to pre­dict how many times a giv­en set of tests should run, I would high­ly sug­gest that in all oth­er cas­es you should ​“clean up” your tests and declare a plan. Later on, if you add or remove tests you’ll imme­di­ate­ly be aware that some­thing has changed and it’s time to tal­ly up a new plan.

What about oth­er Perl test­ing frame­works? They can use plans, too. Here are two examples:

• Test::Class declares its plans as part of the method­’s Test attribute, and uses helper meth­ods called fail_if_returned_early and fail_if_returned_late to indi­cate that an unfol­lowed plan should trig­ger failure.
• Test::Class::Moose says ​“no plans need­ed” but also sup­ports declar­ing plans either in an attribute or via a method call.

Thoughts? Does declar­ing a test plan make writ­ing tests too inflex­i­ble? Does not hav­ing a plan encour­age bad behav­ior? Tell me what you think in the com­ments below.