Spec: partially overriding generators in a map spec

Question

Assuming I have already defined a spec from which I'd like to generate test data:

(s/def :customer/id uuid?)
(s/def :customer/given-name string?)
(s/def :customer/surname string?)
(s/def :customer/age pos?)
(s/def ::customer
  (s/keys
    :req-un [:customer/id
             :customer/given-name
             :customer/surname
             :customer/age]))

In generating test data, I'd like to override how ids are generated in order to ensure they're from a smaller pool to encourage collisions:

(defn customer-generator
  [id-count]
  (gen/let [id-pool (gen/not-empty (gen/vector (s/gen :customer/id) id-count))]
    (assoc (s/gen ::customer) :id (gen/element id-pool))))

Is there a way I can simplify this by overriding the :customer/id generator in my test code and then just using (s/gen ::customer)? So, something like the following:

(with-generators [:customer/id (gen/not-empty (gen/vector (s/gen :customer/id) id-count)))]
  (s/gen ::customer))

Answer 1

Officially, you can override generators for specs by passing an overrides map to s/gen (See the docstring for more details):

(s/def :customer/id uuid?)
(s/def :customer/given-name string?)
(s/def :customer/surname string?)
(s/def :customer/age nat-int?)
(s/def ::customer
  (s/keys
    :req-un [:customer/id
             :customer/given-name
             :customer/surname
             :customer/age]))

(def fixed-customer-id (java.util.UUID/randomUUID))
fixed-customer-id
;=> #uuid "c73ff5ea-8702-4066-a31d-bc4cc7015811"
(gen/generate (s/gen ::customer {:customer/id #(s/gen #{fixed-customer-id})}))
;=> {:id #uuid "c73ff5ea-8702-4066-a31d-bc4cc7015811",
;    :given-name "1042IKQhd",
;    :surname "Uw0AzJzj",
;    :age 104}

Alternatively, there is a library for such stuff named genman, which I developed before :) Using it, you can also write as:

(require '[genman.core :as genman :refer [defgenerator]])

(def fixed-customer-id (java.util.UUID/randomUUID))

(genman/with-gen-group :test
  (defgenerator :customer/id
    (s/gen #{fixed-customer-id})))

(genman/with-gen-group :test
  (gen/generate (genman/gen ::customer)))