Clojure Testing with clojure.test — deftest, is, testing, from REPL to CI | Episode 22

Tests you can run in seconds are tests you'll actually run. In this episode we pin down the `app.util` namespace from Episode 20 — `shout`, `slugify`, `wrap` — with real `clojure.test` assertions. Three `deftest` blocks, seven `is` assertions, and both ways to run them: from the REPL with `run-tests`, and from the command line with `clj -M:test`. We set up two aliases in `deps.edn`: `:dev` adds `test/` to the classpath so your REPL can see the tests, and `:test` wires up the cognitect test runner for CI. Then we drive the full cycle — red, refactor, green — with a failing `is` right in the REPL, showing exactly what `expected` and `actual` look like in place. Student code: https://github.com/GoCelesteAI/clojure-for-beginners/tree/main/episode22 Every keystroke is shown on screen with generous pauses so you can follow along at your own pace. What You'll Learn: - `deftest` — declare a named test - `is` — the single-assertion form - `testing` — label groups of related assertions - `clojure.test/run-tests` — run a test namespace from the REPL - `:dev` alias — `{:extra-paths ["test"]}` so `clj -A:dev` sees your tests - `:test` alias — cognitect test-runner for `clj -M:test` - Red / refactor / green — the inner loop applied to tests - `is` prints FAIL, expected, and actual inline — no separate test UI needed Timestamps: 0:00 - Intro 0:15 - Preview: what you'll write 0:51 - The code under test — app.util 1:16 - The test namespace — util_test.clj 1:38 - deps.edn — :dev and :test aliases 1:53 - Start the REPL with clj -A:dev 2:06 - Load the test namespace 2:18 - run-tests — three tests, seven assertions, zero failures 2:30 - Ad-hoc `is` at the REPL 2:46 - A failing `is` — inline FAIL with expected / actual 3:18 - Control-D 3:25 - Run the whole suite from the CLI — clj -M:test 3:27 - Recap 4:06 - What's next: Episode 23 Key Takeaways: 1. `deftest` declares a test; `is` is a single assertion; `testing` labels a group. 2. A `:dev` alias with `{:extra-paths ["test"]}` lets the REPL see your tests, so you can `(clojure.test/run-tests 'app.util-test)` without restarting. 3. A `:test` alias with `cognitect-labs/test-runner` + `:main-opts` gives you a single-command CI runner: `clj -M:test`. 4. `is` prints FAIL inline with expected and actual — no separate test harness needed during development. 5. Red, refactor, green — applied to a live REPL session — is measured in seconds, not minutes. Phase 4 keeps rolling. Next up: adding a dependency from Clojars. Taught by CelesteAI. Like and subscribe for more Clojure tutorials!