elm-test Basics

• elm-test NPM package
• elm-explorations/test Elm package
• elm-test init command
• Running elm-test finds exposed values of type Test

TDD Principles

• Testing in Elm is easier because it's just expectations of input to output (deterministic)
• TDD is a design practice too
• Programming by Intention
• Writing test first makes code testable & decoupled
• Red, green, refactor
• YAGNI
• "Make the change easy, then make the easy change"
• Kent Beck's TDD by Example
• Here's a staring template of a code kata in Elm that you can use to practice
• Emily Bache has many more code katas you can practice on her GitHub

Fuzz Testing

• Also known as Property-Based Testing

• Martin Janiczek's elm-minithesis project

• elm-test's view testing API includes Test.Html.Query, Test.Html.Selector, and Test.Html.Event

View objects

Testing pyramid

Mocking and stubbing are not needed or possible in Elm

Order dependent test helper in Ruby: i_suck_and_my_tests_are_order_dependent

When to Use Types or Tests

• Jeroen's Safe Unsafe Operations blog post
• Richard Feldman's talk on Types and Tests
• Make Impossible States

Should you test implementation details?

• Discourse thread discussing testing internals
• Think in terms of a modules responsibility

Higher-Level Testing in Elm

elm-program-test

Martin Janiczek's elm Europe talk on testing Msg's with ArchitectureTest

• Richard test-update package