Code coverage in your apps

Ok, so this post isn’t necessarily about geodev, but it’s related in that I’m sure a lot of us don’t write enough tests.

I’m working on this, and I recently, for some odd reason, got really into code coverage and tooling. Using it as a tool to help guide me to focus on writing my tests.

Here is a video I did on Intern with the ArcGIS API for JavaScript.

I tried to write my tests very modularly, focusing on a single unit to test, but even so it may touch other parts of my code, so that helps me figure out hey, maybe this test is too general, so not useful or this percentage of a file is covered by other tests, don’t worry about writing more.

The tools I use:

• Intern
• Istanbul
• remap-istanbul

Here are the npm scripts I use to run my code coverage.

{
    ...
    "coverage:start": "intern run -w --config ./dist/tests/intern-local.js reporters=Pretty reporters=node_modules/remap-istanbul/lib/intern-reporters/JsonCoverage && npm run coverage:after",
    "coverage:after": "npm run coverage:html && npm run coverage:remap && del coverage-final.json && npm run coverage:text && npm run coverage:clean",
    "coverage:clean": "del coverage-mapped.json",
    "coverage:html": "node_modules/.bin/remap-istanbul -i coverage-final.json -t html -o html-report",
    "coverage:remap": "node_modules/.bin/remap-istanbul -i coverage-final.json -o coverage-mapped.json",
    "coverage:text": "istanbul report text",
        ...
}

What the above does, starting with coverage:start runs intern with a webdriver, so Chrome pops up in auto-nutso mode and runs all my tests and also runs with remap-istanbul to create a json report of my code coverage that intern will generate. It’s the remap part that is key to let me know what parts of my source TypeScript files might be missing coverage.

Then from there, I generate an HTML report of the code coverage I can admire and click through and see the actual source code with color highlighting let me know if I have zero or partial coverage of certain functions and branches.

Then I print the results of the coverage to the console because I’m lazy.

There’s some cleanup in there to remove the output json files from my project.

Here is a wiki from remap-istanbul on using it with Intern.

This works out real nicely for me and since I struggled a bit with some of the tooling, like how to use Istanbul, remap-istanbul and some of the APIs and how reports are generated, I thought maybe others could benefit as well.

So go forth and test my friends!