Unit testing your Sublime Text 3 plugin

One advantage of developing in Sublime Text is that you end up sharing the same IDE backends with vim, emacs and atom users.

The Sublime plugins for these backends could be considered little more than glue code. I believe they are worth investing extra time in: They can make or ruin the user experience.

That said, the development experience isn’t great. Your debugging options are:

• Sprinkle print() statements everywhere, restart editor
• Install and trigger legitimate debugger (see this package)

To enable quick iterative development, here follows a short guide on setting up your package for unit testing.

Unit Testing your Sublime Text plugins

The following assumes you have set up a virtualenv (python 3.3 to match ST3), and are working inside the Packages/YourPackage directory.

Create your first test

• Create a ‘test’ subfolder
• Add a test file to it (test/test_myplugin.py):

import unittest
import myplugin

class LoadPluginTest(unittest.TestCase):

	def test_can_load(self):
		myplugin.plugin_loaded()

• Run this test using the ide or the command line: python -m unittest

You should see errors about missing types from sublime and sublime_plugin. We will fix those next:

Fix sublime and sublime_plugin imports

Create two stubs: test/stubs/sublime.py and test/stubs/sublime_plugin.py.

For inspiration, see some simple stubs or a more complete example

Import these stubs wherever your plugin fails to load:

try:
    import sublime
except ImportError:
    from test.stubs import sublime

Fix your own imports

Sublime Text 3 loads your package from it’s Packages/ directory, while your tests run from Packages/YourPackage. The import statements are incompatible when running tests:

# ImportError: No module named YourPackage
from YourPackage.yourmodule import function, class

# SystemError: Parent module '' not loaded, cannot perform relative import
from .yourmodule import function, class

I found this solution in the Sublime ctags plugin.

# add YourPackage/ to the import path.
import sys, os
sys.path.append(os.path.dirname(os.path.realpath(__file__)))

# rest of imports in the usual way:
from yourmodule import function, class

Not every module needs this logic, but it is best to convert them all to normal imports and then fix loading errors in sublime by adding the above.

Fix remaining missing dependencies

Once your plugin loads correctly under test, you can start testing other components, using a combination of more stubs and unittest.mock

Anaconda testing setup

The Anaconda sublime package has some handy testing shortcuts. You’ll need a YourPackage.sublime-project, with the following settings (adjust the virtualenv path):

{
	# other settings
	"settings":
		{
			"test_command": "python -m unittest",
      		"test_virtualenv": "~/.virtualenvs/python3"
		}
	}
}

Travis CI and Coveralls in 3 steps

• Sign up for Travis CI
• Sign up for Coveralls
• Add this .travis.yml to the root of your package:

language: python
python:
  - "3.3"

# command to install dependencies
install:
  - pip install coverage
  - pip install coveralls

# command to run tests
script: coverage run --source="." --omit="test/*" -m unittest

# publish results
after_success: coveralls