The rendering tests use Puppeteer to take a screenshot of a map and compare it to an expected screenshot. Each directory in the cases directory includes a single test case with the following files:

main.js - the script that sets up the map and calls the magic render() function
expected.png - the expected screenshot (this can be generated with the --fix flag)
actual.png - the screenshot generated when running the tests (ignored by git)
pass - a generated marker file that represents the last time the test passed (ignored by git)

Running the tests

To run all the rendering tests:

node rendering/test.js

To run a single rendering test case:

node rendering/test.js --match your-test-case-name

Creating a new test

To create a new test case, add a directory under cases and add a main.js to it (copied from one of the other cases). Then to generate the expected.png screenshot, run the test script with the --fix flag:

node rendering/test.js --match your-test-case-name --fix

Note that your main.js needs to call the magic render() function after setting up the map. This triggers a snapshot. The render() function can be called with an options object that includes a tolerance property. The tolerance is related to the ratio of mismatched pixels to the total number of pixels in the actual screenshot.

After creating a new test case, commit your main.js and expected.png files.