Learn how to write automated tests using Elixir’s built-in ExUnit testing framework.

”Wrong” way of testing

• Manually run code, inspect results by hand—not repeatable or robust

”Right” way (with ExUnit)

• Use Elixir’s built-in ExUnit framework to run automated repeatable tests with mix test

Running tests

• Place tests in the test/ directory
• Run mix test to execute all tests, or specify a file or line to run just those tests

Test structure & conventions

• Use defmodule ...Test and use ExUnit.Case
• Write tests with the test "description" do ... end macro
• assert for checking expectations; refute for negating them

Test scripts & automation

• Can configure test scripts in your mix.exs for consistent workflow
• Tests run in parallel by default for speed (except those that share state or use async: false)

The use macro

• use ExUnit.Case, async: true sets up the test environment
• doctest macro lets you write tests in your docs (@doc), and runs them automatically

Writing practical tests

• Example: Test creating a user with no params returns an error, creating with params works, etc.
• Can pattern match directly in test setup or test assertions for more descriptive, tight checks

Setup/context & callbacks

• Use setup and setup_all for test prep, sharing state/context among multiple tests
• Pattern match on the returned context in individual tests for custom per-test state

Test coverage

• Run with mix test --cover to see which lines of code are tested

Summary

ExUnit is Elixir’s slick, parallel, and repeatable unit/integration testing tool. It offers clear syntax, per-file and per-test targeting, helpful macros (doctest, assert, setup), and keeps your codebase robust, maintainable, and well-documented.