Clojure Spec

Instrumentation

Note: Instrumentation only works for :args in a function definition. :fn and :ret are only used during generative / property based testing.

Here is an example of how this works.

Create a function definitions

(defn adder [x y]
  (+ x y))

(s/fdef adder
  :args (s/cat :x int? :y int?))

If we call adder without instrumentation, we get the following error:

1. Unhandled clojure.lang.ArityException
   Wrong number of args (3) passed to: pine.db.postgres/adder

However, if we need to enable instrumentation:

(ns acme.app
  (:require [clojure.spec.test.alpha :as stest]))

(stest/instrument [`adder])

Now, when we call adder with the wrong arguments, we get a relatively helpful message:

1. Unhandled clojure.lang.ExceptionInfo
   Spec assertion failed.

         Spec: #object[clojure.spec.alpha$regex_spec_impl$reify__2510 0x6c0f16e3 "clojure.spec.alpha$regex_spec_impl$reify__2510@6c0f16e3"]
        Value: (1 2 4)

     Problems:

            val: (4)
             in: [2]
         failed: (cat :x int? :y int?)
         reason: Extra input

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• Tag: clojure