Hypothesis 1.0: A property-based testing library for Python

Post by bowyakka » Mon, Mar 30, 2015, 8:29 PM UTC

DRMacIver wrote: post #9

bowyakka wrote: post #8

This library is awesome, I am a massive fan of randomized and quick-check style testing. This type of testing has for me found so many bugs its surreal. I love the fact that hypothesis is a proper quickcheck and not just the fuzzing part, and that the author has a crazy stack-based-vm-language-testing thing project that might be useful. I have been using this library with py.test for 6 months now and its been a godse…

Thanks so much for the kind words! The best part of this message is that if you were someone I knew and thus could trust to only say nice things about me you would offer to buy me gin instead of beer. ;-)

Post by baq » Mon, Mar 30, 2015, 9:27 PM UTC

DRMacIver wrote: post #7

lgierth wrote: post #6

Is this similar to Mutation Testing, where the code being tested is mutated, in order to identify unspecified behavior? Mutant is a Ruby library for this: https://github.com/mbj/mutant

No, it's much closer to classic fuzz testing, where the test is held constant and the data fed to it is varied. I've been meaning to see if I can figure out a way to use mutation testing to feed into Hypothesis, but it's on the long list of things I'll try "at some point"

Post by e12e » Mon, Mar 30, 2015, 10:05 PM UTC

    @assert(idempotent) #(inv(inv(x))==x)
    def inv(x):
      "Return -x"
      @given(float):
        @assume(not isnan(x))
      return -x

    @assume(not isnan(x)) #implies x is number, but not nan
    @idempotent # inv(inv(x)) == x
    def inv(x):
      return -x

Post by evancordell » Mon, Mar 30, 2015, 10:22 PM UTC

Post by e12e » Tue, Mar 31, 2015, 1:43 AM UTC

reverius42 wrote: post #16

e12e wrote: post #15

Interesting stuff. Can't wait to play with. One immediate reaction from reading about things like "@given(float)... def testFun(x): ... assume(not isnan(x))..." -- I immediately would prefer to decorate/document my functions (that could be test functions, but more generally my "real" functions) with these pre-/post- conditions and assumtions, and generate the tests, something like: @assert(idempotent) #(inv(inv(x))==…

I don't think that's what idempotent means. The only way f can be idempotent when f(f(x)) == x is if f(x) == x. (This implies that f is the identity function). The property that makes the function idempotent is that successive application produces the same result as initial application: f(f(x)) == f(x).