Enable generator to be seeded via the environment #287
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The seed still can't be set by QuickCheck users, but the new Gen constructor is useful for other crates that use QuickCheck only for its Arbitrary trait. Closes BurntSushi#277
This change allows generators in a `QuickCheck` instance to be seeded via the environment. This allows reproducing tests by simply setting the environment variable, e.g. when performing an automated `git bisect`. If implementations of `Arbitrary` do not pull new entropy during generation of values, e.g. by using generators returned by `Gen::new`, that is.
Previously, the configuration parameters were described in prose. Neither the minimum number of valid tests nor any description of the environment variables which could invluence these parameters were covered by the text. Naturally, neither was the recently introduced `QUICKCHECK_SEED`. This change replaces the prose with a list, which includes not only the defaults (where applicable) but also the environment variables consultet during initialization.
neithernut
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This change allows generators in a
QuickCheckinstance to be seeded via the environment. The main motivation is faithfully reproducing tests, i.e. with the same seeds. One common use-case would be automated bisects.For example, a CI system could provide a seed which is stored alongside the report. In the case of failure, that seed could then be used for bisecting, eliminating the chance of falsely flagging a "bad" commit as "good" due to the randomness of input values.
This change is based on #278 (for
Gen::from_seed).What's still missing:
Genwill be used for all runs of a given test, and thus we'll produce different input values for each iteration. But maybe I overlooked something?