Skill: Testing Clojure ClojureScript

Goal

Set up and write tests for Clojure and ClojureScript projects using cljs.test, cljs-init-tests, and shadow-cljs workflow.

Use This Skill When

• Testing Clojure or ClojureScript code

• Setting up test infrastructure for CLJS projects

• Using shadow-cljs for compilation

• The user asks to "add Clojure tests" or "set up cljs.test"

Do Not Use This Skill When

• Testing TypeScript/JavaScript code (use testing-typescript-vitest)

• Project uses a different Clojure test framework (midje, test.check)

ClojureScript Test Setup

shadow-cljs Configuration

;; shadow-cljs.edn {:source-paths ["src" "test"] :dependencies [[cider/cider-nrepl "0.28.5"] [cider/orchard "0.11.0"]]

:builds {:test {:target :browser-test :output-to "target/test/test.js" :tests {:matches #".*-test$"} :devtools {:http-port 8080 :http-resource-root "target/test"}}

      :node-test {:target :node-test
                  :output-to "target/test/node-test.js"
                  :tests {:matches #".*-test$"}}}}

package.json Scripts

{ "scripts": { "test:cljs": "shadow-cljs compile node-test && node target/test/node-test.js", "test:browser": "shadow-cljs compile test && npx http-server target/test -p 8080", "test:watch": "shadow-cljs watch test" } }

Basic cljs.test Syntax

(ns my-project.core-test (:require [cljs.test :refer [deftest is testing are]] [my-project.core :as core]))

(deftest add-test (testing "addition" (is (= (core/add 2 3) 5)) (is (= (core/add -1 1) 0)) (is (= (core/add 0 0) 0))))

(deftest subtract-test (testing "subtraction" (is (= (core/subtract 5 3) 2)) (is (= (core/subtract 3 5) -2))))

(deftest multiply-test (testing "multiplication" (are [x y] (= (core/multiply x y) (* x y)) 2 3 -1 5 0 10)))

Test Assertions

(deftest assertion-examples (testing "basic assertions" (is true) (is (= 1 1)) (is (not false)))

(testing "collection assertions" (is (empty? [])) (is (seq [1 2 3])) (is (contains? {:a 1} :a)) (is (contains? [1 2 3] 0)))

(testing "exception handling" (is (thrown? js/Error (throw (js/Error. "test")))))

(testing "approx assertions for floats" (is (== 0.3 (+ 0.1 0.2)))))

Testing Async Code

(ns my-project.async-test (:require [cljs.test :refer [deftest is testing async]] [my-project.async :as async]))

(deftest async-test (async done (async/timeout 100 (is true)) (done)))

(deftest promise-test (async done (-> (async/load-data) (.then (fn [data] (is (= (:status data) 200)) (done))) (.catch (fn [err] (is false "Should not error") (done))))))

cljs-init-tests Macro

The cljs-init-tests provides convenient initialization for tests:

(ns my-project.init-test (:require [cljs-init-tests.core :refer [init-tests deftest-test]] [my-project.math :as math] [cljs.test :refer [deftest is testing]]))

;; Initialize test infrastructure (init-tests)

;; Test definitions work normally (deftest math-tests (testing "basic math operations" (is (= (math/add 2 3) 5)) (is (= (math/subtract 5 3) 2))))

Setup and Fixtures

(ns my-project.fixtures-test (:require [cljs.test :refer [deftest use-fixtures testing]] [my-project.db :as db]))

;; Define fixtures (defn setup-db [f] (db/reset!) (f) (db/cleanup!))

(defn with-logging [f] (println "Starting test") (f) (println "Finished test"))

;; Use fixtures (use-fixtures :once setup-db) (use-fixtures :each with-logging)

(deftest database-test (testing "database operations" (is (some? (db/connect))) (is (db/insert {:name "test"}))))

Testing CLJS-Specific Features

(ns my-project.cljs-specific-test (:require [cljs.test :refer [deftest is testing]] [cljs.core :as c]))

(deftest atom-test (let [counter (atom 0)] (swap! counter inc) (is (= @counter 1)) (swap! counter inc) (is (= @counter 2))))

(deftest reagent-test (let [component (fn [] [:div "Hello"])] (is (fn? component))))

(deftest protocol-test (let [record (->Record. :field)] (is (= (:field record) :field))))

Shadow-cljs Test Compilation

Test Build Output

Compile for Node.js

shadow-cljs compile node-test

Compile for browser

shadow-cljs compile test

Watch and test

shadow-cljs watch test

CI/CD Integration

#!/bin/bash

run-cljs-tests.sh

set -e

Install dependencies

yarn install

Compile tests

shadow-cljs compile node-test

Run tests

node target/test/node-test.js

Check exit code

if [ $? -eq 0 ]; then echo "Tests passed!" exit 0 else echo "Tests failed!" exit 1 fi

Organization

src/ └── my_project/ ├── core.cljs └── core_test.cljs # Test in same namespace

test/ └── my_project/ ├── integration_test.cljs └── e2e_test.cljs

Best Practices

1. Test Naming

;; GOOD - descriptive test names (deftest add-two-positive-numbers-returns-sum) (deftest handle-empty-input-gracefully)

;; BAD - vague names (deftest test-add) (deftest test-stuff)

2. Test Organization

(deftest arithmetic-tests (testing "addition" (is (= (+ 2 3) 5)) (is (= (+ 0 0) 0)))

(testing "subtraction" (is (= (- 5 3) 2))))

3. Property-Based Testing

;; With test.check (deftest sort-is-idempotent (let [gen (gen/vector gen/int)] (is (forall [v gen] (= (sort v) (sort (sort v)))))))

Running Tests

Command Purpose

shadow-cljs compile test

Compile for browser

shadow-cljs compile node-test

Compile for Node.js

shadow-cljs watch test

Watch and test

shadow-cljs test

Run tests via CLI

Output

• shadow-cljs.edn configuration

• Test namespace setup with cljs.test

• Example test files for CLJS

• Fixtures and setup patterns

• CI/CD test script

References

• cljs.test: https://cljs.github.io/api/cljs.test/

• shadow-cljs: https://shadow-cljs.github.io/docs/

• cljs-init-tests: https://github.com/Olical/cljs-init-tests

• test.check: https://github.com/clojure/test.check

Suggested Next Skills

Check the Skill Graph for the full workflow.

• testing-typescript-vitest