Generate test doubles using clojure.spec
Testing code that has side effects can be painful. Mocking out those interactions is a great way to keep your tests fast and reliable. Using clojure.spec, we can automatically generate those mocks.
Specific depends on Clojure 1.9 (or 1.8 with the clojure.spec backport) and clojure.test. To add the following to your project.clj file to add it to your project.
(defproject sample
:dependencies [[org.clojure/clojure "1.9.0"]]
:profiles {:dev {:plugins [[com.benrady/specific "0.0.1-SNAPSHOT"]]}})
Specific works best with functions that have clojure.spec definitions. You can include these definitions with your code under test, or you can just add them to your tests.
(ns sample)
(defn some-fun [greeting & names]
(spit "fun.txt" (apply str greeting ", " names)))
(clojure.spec/fdef some-fun
:args (clojure.spec/+ string?)
:ret string?)
Assuming we've defined the function above, and its associated spec, there are number of ways to test interactions with it.
Mocking a function prevents the original function from being called, which is useful when you want to prevent side effects in a test, but still want to ensure it was invoked properly. Mocked functions validate their arguments against the specs defined for the original function.
(testing "mock functions"
(with-mocks [sample/some-fun]
(testing "returns a value generated from the spec"
(is (string? (sample/some-fun ""))))
(testing "tracks the arguments of each call"
(sample/some-fun "hello")
(is (= [["hello"]] (calls sample/some-fun))))))
Invoking a mock with arguments that don't meet the spec will result in a failure being reported to the test runner
(testing "reports an error if the arguments do not meet the specs "
(some-fun 3))
;; FAIL in (specific.core) (test_double.clj:8)
;; mock functions tracks the arguments of each call
;; expected: "Calls to specific.sample/some-fun to conform to (ifn?)"
;; actual: "Calls to specific.sample/some-fun were (3)"
### Stub Functions
Stub functions are more leinent than mocks, not requiring the function to have a spec. This is useful when mocking out interactions with functions you did not write.
```clojure
(testing "stub functions"
(with-stubs [spit]
(testing "doesn't need a spec to track calls"
(sample/some-fun "hello" "world")
(is (= [["fun.txt", "hello, world"]] (calls spit))))))
Spy functions call through to the original function, but still record the calls and enforce the constraints in the function's spec. You can make assertions about how the spy was invoked after it is called.
Specify works especially well with generative tests.
Copyright (C) 2016 Ben Rady benrady@gmail.com
This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License version 2 as published by the Free Software Foundation.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
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