testing: generate tests operations using Hypothesis The idea of this patch is to expand the use of Hypothesis within Mercurial to use its concept of "stateful testing". The result is a test which runs a sequence of operations against a Mercurial repository. Each operation is given a set of allowed ways it can fail. Any other non-zero exit code is a test failure. At the end, the whole sequence is then reverified by generating a .t test and testing it again in pure mode (this is also useful for catching non-determinism bugs). This has proven reasonably effective at finding bugs, and has identified two problems in the shelve extension already (issue5113 and issue5112).