Mark Battersby markalfred

Idiomatic React Testing Patterns

Testing React components seems simple at first. Then you need to test something that isn't a pure interaction and things seem to break down. These 4 patterns should help you write readable, flexible tests for the type of component you are testing.

Setup

I recommend doing all setup in the most functional way possible. If you can avoid it, don't set variables in a beforeEach. This will help ensure tests are isolated and make things a bit easier to reason about. I use a pattern that gives great defaults for each test example but allows every example to override props when needed:

	#!/bin/sh

	###
	# SOME COMMANDS WILL NOT WORK ON macOS (Sierra or newer)
	# For Sierra or newer, see https://github.com/mathiasbynens/dotfiles/blob/master/.macos
	###

	# Alot of these configs have been taken from the various places
	# on the web, most from here
	# https://github.com/mathiasbynens/dotfiles/blob/5b3c8418ed42d93af2e647dc9d122f25cc034871/.osx

	section: screens
	desktop:
	laptop:
	end

	section: aliases
	desktop:
	Williams-Mac-Pro.local
	laptop:
	will.local

	# remove the heads off arrays of base_64 encoded datauris
	#
	# in this example we take the array of images encoded from
	# whammy.js and return an array without the heads. This is
	# an admittedly vain optimization but, every byte counts.

	Base64Header = (type) ->
	head: "data:#{type};base64,"
	add: (string) ->
	"#{HEAD}#{string}"

	CHECKING_OUT_BRANCH=$3
	OLD_BRANCH=$1
	NEW_BRANCH=$2

	if [ $CHECKING_OUT_BRANCH -eq 1 ]
	then
	FILES_CHANGED=`git diff $OLD_BRANCH $NEW_BRANCH --name-status`
	MIGRATIONS_REMOVED=`echo "$FILES_CHANGED" \| egrep 'D\tdb/migrate/([0-9]+)' \| sort -r`
	MIGRATIONS_ADDED=`echo "$FILES_CHANGED" \| egrep 'A\tdb/migrate/([0-9]+)'`

	#!/bin/bash
	# This script will install a Git pre-push hook that prevents force pushing the master/main branch.
	# There are three variants that I have built:
	# - pre-push: prevents force-pushing to master/main.
	# - pre-push-2: prevents force-pushing to master/main depending on the remote (you need to edit the file!).
	# - pre-push-3: prevents any type of pushing to master/main.
	# Set the desired version like this before proceeding:
	# FILE=pre-push

	# Single repo installation:

	# Find the longest words you can type, alternating hands at each character. Y and B excluded.

	egrep "^[$right]?([$left][$right]){6,}[$left]?\$" /usr/share/dict/words

	# Qwerty
	left=qwertasdfgzxcv
	right=uiophjklnm

	# Colemak
	left=qwfpgarstdzxcv