A month of Flutter: configuring continuous integration

Abraham Williams December 3, 2018

When starting a new project I like to automate as much as possible. One of the most important tasks is getting tests running on CI. There are a number of great CI services but for this project I'm going with Travis CI.

Let's take a look at the configuration I've settled on and what it all means:

language: dart
dist: xenial
addons:
  apt:
    packages:
    - lib32stdc++6
install:
- git clone https://github.com/flutter/flutter.git -b beta
- ./flutter/bin/flutter doctor
script:
- cd app
- ../flutter/bin/flutter test
cache:
  directories:
  - $HOME/.pub-cache

language tailors the CI environment for a specific language. If you leave this out, the default language is Ruby. This isn't strictly needed as Flutter will actually download its own version of Dart. I specified Dart so that if I write CI tooling in the future, I can do it in Dart.
dist specifies the Ubuntu base version that gets used. Travis currently defaults to Trusty Tahr which is end of life in 2019 so I'm specifying Xenial Xerus which is supported until 2021.
addons lets you have additional packages installed on the OS. In my experimentation, tests still pass without lib32stdc++6 but flutter doctor complains so I'm including it anyway.
install would typically call Dart's pub get but Flutter complains so we'll just override that and install Flutter instead.
script is where we run the tests. Not that the Birb app is in the app directory so we have to cd into it first.
cache is the final bit. This tells Travis to cache the contents of the default Dart package cache. This should make it faster for Flutter to install the app's dependencies.

This configuration runs great and takes about 2 minutes 30 seconds on the base app.

I also tried caching the flutter directory to boost install speed. Here is an configuration iteration I tried:

install:
- |
    if [ ! -d flutter ] ; then
      git clone https://github.com/flutter/flutter.git -b beta
    fi
- ./flutter/bin/flutter doctor

cache:
  directories:
  - flutter
  - $HOME/.pub-cache

Caching the flutter directory dropped the test run time to to about 1 minute 10 seconds! The install step was then more complex as it has to check if the flutter directory exists and only run git clone if it doesn't. But there was a larger issue where the "if directory does not exist" was having false positives and causing Flutter to not get installed correctly. I would like to improve CI performance but don't want to spend any more time on it now so I've added #6 Cache flutter directory on CI to the backlog as a future improvement.

With CI setup, I like to protect the master branch from accidental pushes. This is less important when you are working on your own but is very important when working with teams. It's also a good way to require that tests are kept in a passing state.

This is how I configured GitHub's branch protection on the master branch:

Configuring master as a protected branch on GitHub