Invalid examples in simple cases

[Jonathan Berthias]

Hi,

I'm not sure if this was asked before (couldn't find it though), but I would like some details about what the invalid examples are.

I am running hypothesis with the pytest --hypothesis-show-statistics flag. the docs show this snippet:

@given(st.integers())
def test_integers(i):
     pass

which yields the following stats:

100 passing examples, 0 failing examples, 0 invalid examples

However, changing the `st.integers()` to `st.floats()` yields some invalid examples:

100 passing examples, 0 failing examples, 2 invalid examples

Could you explain why that is? I thought invalid examples were due to failing filters or assume statements, but it seems even plain data generation can create them.

Thanks,

Jonathan

[Zac Hatfield Dodds]

Hi Jonathan,

https://hypothesis.works/articles/how-hypothesis-works/ explains a bit about Hypothesis' underlying model of "parsing examples from choices" (usually random bytes).  

The invalid examples here are because the `st.floats()` strategy will sometimes try generating particularly weird examples from an internal list, and so it's possible to end up rejecting an example because it repeatedly tries to generate e.g. the fourth of three weird edge cases.  `st.integers()` will do the same thing, if you specify two endpoints!

Cheers,

Zac

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