Getting Clojure

Checking Properties

The final piece of the property-based testing puzzle is expressing the property. Happily, test.check provides a lovely syntax for doing just that. To start with a simple example, here we’re stating that each positive integer is smaller than the next positive integer:

test/sample_generators.clj

(prop/for-all [i gen/pos-int]
  (< i (inc i)))

But we’re not quite done: since we’re defining a test and not a theorem, we need to supply a limit on the number of integers we’ll try. Here we pare the infinite run of positive integers down to the first 50 produced by the pos-int generator:

(tc/quick-check 50
  (prop/for-all [i gen/pos-int]
    (< i (inc i))))

There, the quick-check function will check the property that we specified for ...