XML FeedsWriting tests for code is just as important as writing the code itself. Time spent writing tests is less time spent tracking down and fixing bugs, making it a great investment. Despite knowing this it can sometimes be hard to force yourself to stop coding and write tests. Fortunately, Perl has some modules to make it pretty simple. Here's the module we're going to be testing:
As you can see, we have a simple class with one method, add, which adds together all the arguments passed to it. We now need to define a test file for this module, called mymaths.t:
- #!/usr/bin/perl
- use Test::More tests=>6;
- use MyMaths;
- $mymaths = new MyMaths;
- is( $mymaths->add(1,2,3), 6, "1 + 2 + 3 = 6");
- is( $mymaths->add(6,2), 8,"6 + 2 = 8");
- is( $mymaths->add(1,2,3,4), 10, "1 + 2 + 3 + 4 = 10");
- is( $mymaths->add(1,2), 3, "1 + 2 = 3");
- is( $mymaths->add(2), 2, "2 = 2");
- is( $mymaths->add(2,-1), 1, "2 + -1 = 1");
This test file uses the is() method of the builtin Test::More module. This method takes 3 arguments: the test, the expected result and a description. If a test fails, is() will give some feedback on the test.
edit: To run the tests use the `prove` utility which is part of the Test::Harness package:
prove -v mymaths.t
Run all tests in the current directory with:
prove -v .
To run the tests we use another builtin module, Test::Harness. Create tests.pl:
- #!/usr/bin/perl
- use Test::Harness qw(&runtests);
- @tests = @ARGV ? @ARGV : <*.t>;
- runtests @tests;
This script can either be run with a list of test files as arguments, or with no arguments to run all test files. Running the script results in:
- ./mymaths.t ..
- 1..6
- ok 1 - 1 + 2 + 3 = 6
- ok 2 - 6 + 2 = 8
- ok 3 - 1 + 2 + 3 + 4 = 10
- ok 4 - 1 + 2 = 3
- ok 5 - 2 = 2
- ok 6 - 2 + -1 = 1
- ok
- All tests successful.
- Files=1, Tests=6, 0 wallclock secs ( 0.01 usr 0.02 sys + 0.02 cusr 0.01 csys = 0.06 CPU)
- Result: PASS
Everything went fine, as expected. Now go back to the original class definition and make a typo on line 22, so it reads = instead of += and rerun the tests:
- ./mymaths.t ..
- 1..6
- not ok 1 - 1 + 2 + 3 = 6
- not ok 2 - 6 + 2 = 8
- not ok 3 - 1 + 2 + 3 + 4 = 10
- not ok 4 - 1 + 2 = 3
- ok 5 - 2 = 2
- not ok 6 - 2 + -1 = 1
- # Failed test '1 + 2 + 3 = 6'
- # at ./mymaths.t line 7.
- # got: '3'
- # expected: '6'
- # Failed test '6 + 2 = 8'
- # at ./mymaths.t line 8.
- # got: '2'
- # expected: '8'
- # Failed test '1 + 2 + 3 + 4 = 10'
- # at ./mymaths.t line 9.
- # got: '4'
- # expected: '10'
- # Failed test '1 + 2 = 3'
- # at ./mymaths.t line 10.
- # got: '2'
- # expected: '3'
- # Failed test '2 + -1 = 1'
- # at ./mymaths.t line 12.
- # got: '-1'
- # expected: '1'
- # Looks like you failed 5 tests of 6.
- Dubious, test returned 5 (wstat 1280, 0x500)
- Failed 5/6 subtests
- Test Summary Report
- -------------------
- ./mymaths.t (Wstat: 1280 Tests: 6 Failed: 5)
- Failed tests: 1-4, 6
- Non-zero exit status: 5
- Files=1, Tests=6, 0 wallclock secs ( 0.03 usr 0.00 sys + 0.03 cusr 0.00 csys = 0.06 CPU)
- Result: FAIL
Most of the tests failed and gave good feedback to help find the problem.
Summary
Although writing tests can be a chore it is worth doing. If you write tests a little at a time:
- When you design a class.
- When you add a method to a class.
- When you find a bug.
You'll develop a good library of tests without too much effort.
Further reading: Test::More perldoc
Nice article about the basics of using the perl testing modules. You can get away, however, without writing your own test.pl to run the tests by using the prove app instead, which is included in modern perls. It provides a lot of nice features for running the tests such as simple verbose mode and outputting the results with color.
Very nice, thank you for bringing that to my attention! 
I don't want to be negative, it's wonderful that you're introducing Test::More to people who may not have come across it before.
I am happy to see people outside the Ironman bloggers ( http://ironman.enlightenedperl.org/ ) write about Perl and about testing Perl.
wow this is pretty epic. I don't really know that there's a module for testing perl scripts. don't really know TTD as I hack all the way to get my work than. But this might be a good introductory read to get an overview of how things work
A couple of things I noticed
Great article, thanks. It shows how easy it is to write tests with perl. I wish instead of showing the tests.pl with the Test::Harness stuff, you showed that you can just run:
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