Setup Jest test coverage

[HonkingGoose]

What feature would you like to have?

Currently we don't know how much of our code is covered by tests.

After some setup work, we can run Jest with the --coverage true flag to get a Coverage Summary at the end of the run:

=============================== Coverage summary ===============================
Statements   : 100% ( 24413/24413 )
Branches     : 98.11% ( 7964/8117 )
Functions    : 100% ( 2919/2919 )
Lines        : 100% ( 23986/23986 )
================================================================================

Test Suites: 385 passed, 385 total
Tests:       6978 passed, 6978 total
Snapshots:   2002 passed, 2002 total
Time:        600.264 s
Ran all test suites.

What problem will this feature solve?

Know which parts of code are covered by tests.

Once we have covered enough of our code with tests, we can set coverageThreshold ¹ in Jest. This means that future code should always be covered with tests, or the coverage will drop below the threshold and Jest will fail the tests.

Do you want to help make the feature?

Yes

Is there anything else we need to know?

The Jest documentation explains how to set up the coverage reports.

https://jestjs.io/docs/configuration

Footnotes

1. https://jestjs.io/docs/configuration#coveragethreshold-object ↩