propcheck brings property based testing to elisp.
It's similar to the excellent Hypothesis library for Python.
Status: beta. It works, but expect rough edges.
Tests are defined with propcheck-deftest, which defines an ERT test
just like ert-deftest.
Your test should generate input values with the propcheck generator
functions, then call propcheck-should to make assertions about the
result.
(require 'propcheck)
(defun buggy-zerop (num)
;; Return t for all values >= 0. This is wrong! We'll claim that 42
;; is zero.
;;
;; There are lots of numbers that produce a wrong result from this
;; function, but 1 is the smallest. Ideally propcheck would report 1
;; as failing example. It usually does.
(>= num 0))
(propcheck-deftest buggy-zerop-should-match-zerop ()
;; The body of this test will be evaluated repeatedly (up to
;; `propcheck-max-examples` times). The value generated will be
;; different on each iteration.
;;
;; If the assertion ever fails, propcheck will call the body again
;; with progressively smaller values, then report the smallest
;; failing example it could find.
(let* ((i (propcheck-generate-integer "i")))
(propcheck-should
(eq (zerop i)
(buggy-zerop i)))))propcheck provides the following generators:
propcheck-generate-boolpropcheck-generate-integerpropcheck-generate-floatpropcheck-generate-ascii-charpropcheck-generate-proper-listpropcheck-generate-vectorpropcheck-generate-stringpropcheck-generate-one-of
Generally you'll want to use propcheck-deftest to handle seeds for
you. You can still experiement with generator functions in M-x ielm
if you bind propcheck-seed first. Here's an example:
(let ((propcheck-seed (propcheck-seed)))
(propcheck-generate-string nil)) ; e.g. "M26gM{^*v "