How to generate potentially malformed uuids?

[drewgingerich]

I have a function that filters an array of strings to remove invalid uuids. To test this, I'm looking for a way to generate uuids that occasionally generates an invalid uuid. The fc.uuid function appears to only generate valid uuids, but the fc.string function will effectively never generate a valid uuid. Is there a way to generate string values that are often uuids, but sometimes not? I'm new to property-based testing, should I be approaching this differently?

[dubzzz]

What would you consider as an ok generator? Actually not being a valid uuid is wide, a random string is not an uuid, an uuid-looking string with some "g"... In fast-check for now, one way to generate a non-uuid is to do something like that:

fc.string().filter(v => isNotUuid(v))

But you might be too far from an uuid. Otherwise you can play with things such as:

fc.tuple(fc.string(), fc.uuid(), fc.string()).map(([s1, u, s2]) => `${s1}${u}${s2}`).filter(v => isNotUuid(v))

Or even more advanced things where you take only a subpart of the u. You could also play with stringMatching.

[dubzzz]

The most appropriate thing will probably be: #4012. But not yet planned.

[gruhn]

How about randomly choosing between fc.string and fc.uuid ?

const sometimesUuid = fc.oneof(fc.string(), fc.uuid())

With that you get a valid UUID ~50% of the time. If you want a different ratio, you can tweak the weight parameter.

for (const item of fc.sample(sometimesUuid, 20)) {
  console.debug(item)
}

X~GE>~HD{
eString
fffffff6-ffeb-8fff-8000-001098c1bddc
ffffffef-6e8d-7a4b-8f3a-18cdb7b807d5
ffffffed-000d-1000-8000-00010000001a
NSI wUHnc
!"V
5w;3
c15bbc7a-c112-7422-8000-00160000000a

0000000f-7e76-274a-8000-00078b1fe946
ba8d9bb5-0003-1000-bdd0-d2334ba6f53e
f85f494d-1900-63cf-8000-0012ffffffe3
cb742c5d-e7c4-4d9c-9640-5442fffffff0
5ee3736f-cf8e-838d-8000-001600000019
ZHR\}
(!EN!#|%
fffffff0-322e-41d3-938d-92ee67938722
#
}&

If you want the invalid UUIDs to only be broken in certain ways, you can additionally constrain fc.string:

// e.g. length should match valid UUID but we allow arbitrary characters:
const invalidUuid = fc.string({ minLength: 36, maxLength: 36 })
const sometimesUuid = fc.oneof(invalidUuid, fc.uuid())

for (const item of fc.sample(sometimesUuid, 20)) {
  console.debug(item)
}

##x~4M_!z4zz`R#4!#{o!{$~L!3"!8$G""b#
00000017-903f-80c6-9c85-07ba0000001e
26d03f3d-0015-1000-8000-00189f85de57
oUC}K8["$-J%#!$q%.IP{%"x&xf"Oy3$$W" 
0000001a-fff3-8fff-8000-001dffffffe1
4&@1F0U${$|N{L/L~ a #"X$j$szz!]x1' q
e24a4a41-9055-3ef1-bbc2-3606ffffffe0
" %%x |&y#e?{z4xPt%F!y~w8~~bj1CJ0#=R
"!{yUy"H6$&q%xuVH~#zx]QrD{,|zUl$U&!>
580d9c30-4e36-267e-bbb9-cd2c0000001b
3~T)<!8K# ""&S"--{"By(F+!qFu{#.VA  ;
00000012-0003-1000-bc97-39fcffffffe9
a78ec785-7de6-2569-bfb7-0fde100ca557
~_"vlh2xS5"}/b~JZ-{Bp"<=n!z%E\&!L!}%
a0b52ba1-5acb-322e-a362-788ec3e57d17
?N($!!$aY~&J4(C+&7ua""A^j'"Qmy$<%`jU
C' 6yZ0D#(%>hB$7meQ2|xt#3lp6DyW^%-~&
0000001c-19e4-2fa9-85ee-2cf7cc47cc35
$}&D8 #|@I*#(~$mw$T$:zT=Zd~cTV\g"&[!
"9#FDD^BBXH x}+Kth$Z'7\hq#R9${|$3ML#

[drewgingerich]

Thank you, this is exactly what I was looking for. I'm still learning both property-based testing as a concept and fast-check, and I overlooked fc.oneof in the docs!