I can't seem to get the FSCheck shrinker to work. Say I have this
let arb_chars =
Arb.fromGenShrink(
Arb.generate<char[]>,
fun cs -> seq {
printfn "shrinking..."
for i in 0..(cs.Length) do
printfn " shrink %d" i
yield [| cs.[0] |]
})
let prop_len() = gen {
//let! a = Arb.generate<char[]> // this doesn't work either...
let! a = arb_chars.Generator
let len = a.Length
printfn "a.Length = %A" len
return (len <> 5)
}
:
Check.One(config, prop_len)
When I run it, I always get 0 shrinks. Here's a typical run:
a.Length = 0
a.Length = 4
a.Length = 1
a.Length = 0
a.Length = 4
a.Length = 7
a.Length = 6
a.Length = 7
a.Length = 19
a.Length = 18
a.Length = 5
Falsifiable, after 11 tests (0 shrinks) (StdGen (19971972,296557937)):
Original:
<null>
Use Prop.ForAll
to define your property and use the custom generator/shrinker. Something like this (sorry typing from memory but should be close)
let prop_len = Prop.ForAll (arb_chars)
(fun a ->
let len = a.Length
printfn "a.Length = %A" len
return (len <> 5)
)
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