How to set up Travis CI to use linked (local) packages?

I solved this by replicating my development set-up on Travis.

The key to solving this involves giving Travis a way to access GitHub. To do this, log in to GitHub and go to the Personal access tokens page.

You’ll see a form with a field for the name of your token and what permissions you want to grant access to. Fill in a name such as "Travis CI Pull Repo" and select the "repo" section. None of the others are necessary, so no need to give access to them. At the bottom of the page is a green button "Generate token."

Back in your code editor, create a .travis.yml file in the root directory of your project if you don’t have one already. We will be using a RubyGem for the next step, so if you don’t have Ruby gems installed, you’ll need to download it. You can check if you have it installed by running gem -v in the terminal.

If you do, run the following in the terminal to install the Travis RubyGem:

gem install travis

Next, in the terminal, make sure you’re working in your project’s root directory, and use the Travis gem to add the access token to your .travis.yml file:

travis encrypt GH_TOKEN="token-from-github-goes-here" --add

If you were successful, your .travis.yml file should have a bunch of random text an encrypted token saved:

env:
  global:
    secure: "lots-of-seemingly-random-characters"

That’s it! Travis should now be able to pull (and push if that’s what you’re into) to your GitHub repository.

Obviously your .travis.yml file can vary greatly from mine, but at it’s most basic, I set up .travis.yml like this:

language: node_js
node_js:
- '6'
cache:
  directories:
    - node_modules
install:
- npm install
script:
- npm run lint
- npm run test
env:
  global:
    secure: "lots-of-seemingly-random-characters"

To add the cloning and linking of the dependency, add a before_install section with the following commands:

before_install:
- git config credential.helper "store --file=.git/credentials"
- echo "https://${GH_TOKEN}:@github.com" > .git/credentials
- cd ..
- git clone https://github.com/my-name/my-dependency.git my-dependency
- cd my-dependency
- npm install
- npm link
- cd ../my-main-project

What is this actually doing?

1. We configure Git to use our saved access token.
2. We go one directory up and clone the repository into a new folder with the same name as the repository.
3. We go into the repository and install its dependencies. We create a global NPM link.
4. Finally, we return to the main project (the one we are running Travis on). Note that this name must match the repository’s name on GitHub as that’s the name Travis will use.

In addition, we’ll need to actually use the link created above, so in the install section add the following line:

install:
- npm install
- npm link my-dependency

Make sure you put npm link after npm install as by default npm install will obliterate any links (a very annoying bug for those of us who use npm link).