The Hypothesis Example Database¶
When Hypothesis finds a bug it stores enough information in its database to reproduce it. This enables you to have a classic testing workflow of find a bug, fix a bug, and be confident that this is actually doing the right thing because Hypothesis will start by retrying to example that broke things last time.
The database is best thought of as a cache that you never need to invalidate: Information may be lost when you upgrade a Hypothesis version or change your test, so you shouldn’t rely on it for correctness - if there’s an example you want to ensure occurs each time then there’s a feature for including them in your source code - but it helps the development workflow considerably by making sure that the examples you’ve just found are reproduced.
The default (and currently only) storage format is as rather weirdly unidiomatic JSON saved in an sqlite3 database. The standard location for that is .hypothesis/examples.db in your current working directory. You can override this, either by setting either the database_file property on a Settings object (you probably want to specifiy it on Settings.default) or by setting the HYPOTHESIS_DATABASE_FILE environment variable.
Note: There are other files in .hypothesis but everything other than the examples.db will be transparently created on demand. You don’t need to and probably shouldn’t check those into git. Adding .hypothesis/eval_source to your .gitignore or equivalent is probably a good idea.
Upgrading Hypothesis and changing your tests¶
The design of the Hypothesis database is such that you can put arbitrary data in the database and not get wrong behaviour. When you upgrade Hypothesis, old data might be invalidated, but this should happen transparently. It should never be the case that e.g. changing the strategy that generates an argument sometimes gives you data from the old strategy.