gistfile1.txt

OK! So I wrote my code and it's looking good. There's my incredible sum function:

module Sum {
   sub sum($a, $b) is export {
      $a + $b
   }
}
Great, isn't it?! Let's use it:

use Sum;
say sum 2, 3; # 5
That works! I used that to sum the number 2 with the number 3 as you saw. If you read carefully the function you'll see the variables $a and $b haven't a type set. If you don't type a variable it's, by default, of type Any. 2 and 3 are Ints... Ints are Any. So that's OK! But do you know what's Any too? Str (just a example)!

Let's try using strings?

use Sum;
say sum "bla", "ble";
I got a big error:

Cannot convert string to number: base-10 number must begin with valid digits or '.' in '⏏bla' (indicated by ⏏)
  in sub sum at sum.p6 line 1
  in block  at sum.p6 line 7

Actually thrown at:
  in sub sum at sum.p6 line 1
  in block  at sum.p6 line 7
Looks that it do not accept Strs... I don't think Any is the best type in this case.

I didn't think every possibility of arguments. In some cases it's difficult to imagine every possibility. But there's a module to help us with that! Test::Fuzz is a perl6 module that implements the "technique" of generative testing/fuzz testing.

Generative testing or Fuzz Testing is a technique of generating random/extreme data and using this data to call the function being tested.

Test::Fuzz gets the signature of your functions and decides what generators it should use to test it. After that it runs your functions giving it (100, by default) entry data and testing if it will break.

To test that our function, its simple like doing this:

module Sum {
   use Test::Fuzz;
   sub sum($a, $b) is export is fuzzed {
      $a + $b
   }
}
sub MAIN(:$fuzz!) {
   Test::Fuzz.instance.run-tests
}
And run:

perl6 Sum.pm6 --fuzz
It'll show a lot of errors:

Use of uninitialized value of type Thread in numeric context
  in sub sum at Sum.pm6 line 4
Use of uninitialized value of type int in numeric context
  in sub sum at Sum.pm6 line 4
    ok 1 - sum(Thread, int)
Use of uninitialized value of type X::IO::Symlink in numeric context
  in sub sum at Sum.pm6 line 4
    ok 2 - sum(X::IO::Symlink, -3222031972)
Use of uninitialized value of type X::Attribute::Package in numeric context
  in sub sum at Sum.pm6 line 4
    ok 3 - sum(X::Attribute::Package, -9999999999)
Use of uninitialized value of type Routine in numeric context
  in sub sum at Sum.pm6 line 4
    not ok 4 - sum(áéíóú, (Routine))
...
What that means?

That means we should use one of the big features of perl6: Gradual typing. And $a and $b should have a types.

So, let's modify the function and test again:

module Sum {
   use Test::Fuzz;
   sub sum(Int $a, Int $b) is export is fuzzed {
      $a + $b
   }
}
sub MAIN(:$fuzz!) {
   Test::Fuzz.instance.run-tests
}
    ok 1 - sum(-2991774675, 0)
    ok 2 - sum(5471569889, 7905158424)
    ok 3 - sum(8930867907, 5132583935)
    ok 4 - sum(-6390728076, -1)
    ok 5 - sum(-3558165707, 4067089440)
    ok 6 - sum(-8930867907, -5471569889)
    ok 7 - sum(3090653502, -2099633631)
    ok 8 - sum(-2255887318, 1517560219)
    ok 9 - sum(-6085119010, -3942121686)
    ok 10 - sum(-7059342689, 8930867907)
    ok 11 - sum(-2244597851, -6390728076)
    ok 12 - sum(-5948408450, 2244597851)
    ok 13 - sum(0, -5062049498)
    ok 14 - sum(-7229942697, 3090653502)
    not ok 15 - sum((UInt), 1)

    # Failed test 'sum((UInt), 1)'
    # at site#sources/FB587F3186E6B6BDDB9F5C5F8E73C55195B73C86 (Test::Fuzz) line 62
    # Invocant requires an instance of type Int, but a type object was passed.  Did you forget a .new?
...
A lot of OKs!  \o/

But there're still some errors... We can't sum undefined values... So, let's change it again!

module Sum {
   use Test::Fuzz;
   sub sum(Int:D $a, Int:D $b) is export is fuzzed {
      $a + $b
   }
}
sub MAIN(:$fuzz!) {
   Test::Fuzz.instance.run-tests
}
    ok 1 - sum(6023702597, -8270141809)
    ok 2 - sum(-8270141809, -3762529280)
    ok 3 - sum(242796759, -7408209799)
    ok 4 - sum(-5813412117, -5280261945)
    ok 5 - sum(2623325683, 2015644992)
    ok 6 - sum(-696696815, -7039670011)
    ok 7 - sum(1, -4327620877)
    ok 8 - sum(-7712774875, 349132637)
    ok 9 - sum(3956553645, -7039670011)
    ok 10 - sum(-8554836757, 7039670011)
    ok 11 - sum(1170220615, -3)
    ok 12 - sum(-242796759, 2015644992)
    ok 13 - sum(-9558159978, -8442233570)
    ok 14 - sum(-3937367230, 349132637)
    ok 15 - sum(5813412117, 1170220615)
    ok 16 - sum(-7408209799, 6565554452)
    ok 17 - sum(2474679799, -3099404826)
    ok 18 - sum(-5813412117, 9524548586)
    ok 19 - sum(-6770230387, -7408209799)
    ok 20 - sum(-7712774875, -2015644992)
    ok 21 - sum(8442233570, -1)
    ok 22 - sum(-6565554452, 9999999999)
    ok 23 - sum(242796759, 5719635608)
    ok 24 - sum(-7712774875, 7039670011)
    ok 25 - sum(7408209799, -8235752818)
    ok 26 - sum(5719635608, -8518891049)
    ok 27 - sum(8518891049, -242796759)
    ok 28 - sum(-2474679799, 2299757592)
    ok 29 - sum(5356064609, 349132637)
    ok 30 - sum(-3491438968, 3438417115)
    ok 31 - sum(-2299757592, 7580671928)
    ok 32 - sum(-8104597621, -8158438801)
    ok 33 - sum(-2015644992, -3)
    ok 34 - sum(-6023702597, 8104597621)
    ok 35 - sum(2474679799, -2623325683)
    ok 36 - sum(8270141809, 7039670011)
    ok 37 - sum(-1534092807, -8518891049)
    ok 38 - sum(3551099668, 0)
    ok 39 - sum(7039670011, 4327620877)
    ok 40 - sum(9524548586, -8235752818)
    ok 41 - sum(6151880628, 3762529280)
    ok 42 - sum(-8518891049, 349132637)
    ok 43 - sum(7580671928, 9999999999)
    ok 44 - sum(-8235752818, -7645883481)
    ok 45 - sum(6460424228, 9999999999)
    ok 46 - sum(7039670011, -7788162753)
    ok 47 - sum(-9999999999, 5356064609)
    ok 48 - sum(8510706378, -2474679799)
    ok 49 - sum(242796759, -5813412117)
    ok 50 - sum(-3438417115, 9558159978)
    ok 51 - sum(8554836757, -7788162753)
    ok 52 - sum(-9999999999, 3956553645)
    ok 53 - sum(-6460424228, -8442233570)
    ok 54 - sum(7039670011, -7712774875)
    ok 55 - sum(-3956553645, 1577669672)
    ok 56 - sum(0, 9524548586)
    ok 57 - sum(242796759, -6151880628)
    ok 58 - sum(7580671928, 3937367230)
    ok 59 - sum(-8554836757, 7712774875)
    ok 60 - sum(9524548586, 2474679799)
    ok 61 - sum(-7712774875, 2450227203)
    ok 62 - sum(3, 1257247905)
    ok 63 - sum(8270141809, -2015644992)
    ok 64 - sum(242796759, -3937367230)
    ok 65 - sum(6770230387, -6023702597)
    ok 66 - sum(2623325683, -3937367230)
    ok 67 - sum(-5719635608, -7645883481)
    ok 68 - sum(1, 6770230387)
    ok 69 - sum(3937367230, 7712774875)
    ok 70 - sum(6565554452, -5813412117)
    ok 71 - sum(7039670011, -8104597621)
    ok 72 - sum(7645883481, 9558159978)
    ok 73 - sum(-6023702597, 6770230387)
    ok 74 - sum(-3956553645, -7788162753)
    ok 75 - sum(-7712774875, 8518891049)
    ok 76 - sum(-6770230387, 6565554452)
    ok 77 - sum(-8554836757, 5356064609)
    ok 78 - sum(6460424228, 8518891049)
    ok 79 - sum(-3438417115, -9999999999)
    ok 80 - sum(-1577669672, -1257247905)
    ok 81 - sum(-5813412117, -3099404826)
    ok 82 - sum(8158438801, -3551099668)
    ok 83 - sum(-8554836757, 1534092807)
    ok 84 - sum(6565554452, -5719635608)
    ok 85 - sum(-5813412117, -2623325683)
    ok 86 - sum(-8158438801, -3937367230)
    ok 87 - sum(5813412117, -46698532)
    ok 88 - sum(9524548586, -2474679799)
    ok 89 - sum(3762529280, -2474679799)
    ok 90 - sum(7788162753, 9558159978)
    ok 91 - sum(6770230387, -46698532)
    ok 92 - sum(1577669672, 6460424228)
    ok 93 - sum(4327620877, 3762529280)
    ok 94 - sum(-6023702597, -2299757592)
    ok 95 - sum(1257247905, -8518891049)
    ok 96 - sum(-8235752818, -6151880628)
    ok 97 - sum(1577669672, 7408209799)
    ok 98 - sum(349132637, 6770230387)
    ok 99 - sum(-7788162753, 46698532)
    ok 100 - sum(-7408209799, 0)
    1..100
ok 1 - sum
No errors!!!

Test::Fuzz is under development and isn't on perl6 ecosystem yet. And it's needing some help!