Refactoring large test suite - separating data from code

If you follow through the request at the end of the previous part, you now have a test script with lots of tests. You might have noticed and got fed up with the repetition in that code.

Let's try to simplify that by separating the test data from the test code.

Enlarged test script

I know it has not been enlarged by a lot, just enough to feel that all those lines have a lot of similarity.

use strict;
use warnings;

use FindBin qw($Bin);
use lib "$Bin/lib";
use MyCalc;

use Test::Simple tests => 5;

ok sum(1, 1) == 2,    'sum(1, 1) = 2';
ok sum(2, 2) == 4,    'sum(2, 2) = 4';
ok sum(2, 2, 2) == 6, 'sum(2, 2, 2) = 6';

# negative numbers
ok sum(-1, -1)  == -2, 'sum(-1, -1) = -2';

# edge cases:
ok sum(1, -1)   == 0,  'sum(1, -1) = 0';

Move test data to an array

We move all the test data to an array called @cases. Each element of the array is itself a reference to an array. In these internal arrays, the first value is always the expected result, and all the other values are the input to the sum function. Then we have a loop going over the internal array references one-by-one. In each iteration we dereference the array-ref and copy the values from it to $exp, the expected value, and @params, the parameters to be passed to sum`.

use strict;
use warnings;

use FindBin qw($Bin);
use lib "$Bin/lib";
use MyCalc;

my @cases = (
    [2,  1, 1],
    [4,  2, 2],
    [6,  2, 2, 2],
# negative numbers
    [-2, -1, -1],
# edge cases:
    [0,  1, -1],
);

use Test::Simple tests => 5;

for my $c (@cases) {
    my ($exp, @params) = @$c;
    ok sum(@params) == $exp
}

If we run perl test.pl we'll get the following:

1..5
ok 1
ok 2
not ok 3
#   Failed test at test.pl line 22.
ok 4
ok 5
# Looks like you failed 1 test of 5.

That looks almost ok, except that we have lost the test descriptions. We could put those in the @case array as well, but because in this case all the test descriptions are uniform, we can even generate them on the fly:

    my $descr = 'sum(' . join(', ', @params) . ") == $exp";
    ok sum(@params) == $exp, $descr;

The full test.pl now looks like this:

use strict;
use warnings;

use FindBin qw($Bin);
use lib "$Bin/lib";
use MyCalc;

my @cases = (
    [2,  1, 1],
    [4,  2, 2],
    [6,  2, 2, 2],
# negative numbers
    [-2, -1, -1],
# edge cases:
    [0,  1, -1],
);

use Test::Simple tests => 5;

for my $c (@cases) {
    my ($exp, @params) = @$c;
    my $descr = 'sum(' . join(', ', @params) . ") == $exp";
    ok sum(@params) == $exp, $descr;
}

This is much cleaner than we had earlier, and the data (the content of @cases) is almost totally separate from the code that executes it. There is a little issue, though, that might bother you as a programmer if you like DRY. Do you know what it is?