rifftron

rifftron is an R wrapper for difftron, which makes it easy to detect changes in visual output. To use rifftron you currently need to be using git, github and travis-ci.

Basic principles

difftron is a web service that makes it easy to compare images over time. This is particularly useful when testing graphical output, because it makes it easy to see if there have been any changes. Images in difftron are organised into projects and imagesets. Rifftron provides a set of conventions to make it easy to use difftron from R:

• a project corresponds to a package.

• an imageset is the git sha1 hash, unless you have uncommited changed, in which it's called "draft". (This makes it easy to your draft code to the last commit).

• visual tests are R files that live in tests/rifftron. You can arrange your files however you like, but they will be sourced in alphabetical order, and you should use capture_plot() to name and capture graphics that you want to compare over time.

Use test_dir("tests/rifftron") to run tests locally, and compare to the last official commit.

Getting started

1. Sign up for an account at https://difftron.com/.

2. Capture your api key and save it in an env var called DIFFTRON_KEY. The easiest way to do that is to add it to ~/.Renviron:

   DIFFTRON_KEY=mykey
   

   If you want to use different keys for different projects/packages you can put it an .Renviron in the project directory.

Travis

rifftron is designed to be run from a continuous integration system like travis. To get this set up, first create tests/difftron.R:

library(rifftron)
riff_travis()

Next, securely add your difftron key to your travis script by running travis encrypt, then typing DIFFTRON_KEY="your-key" and copying the results into .travis.yml, like:

env:
  global:
    secure: "output from travis encrpyt..."

Now every time that travis runs R CMD check, it will upload your test graphics to a new imageset labelled with the first 10 characters of the git sha hash.