Setting up Environment Variables in Mocha

When running TypeScript tests using the great mocha library, you may want to set environment variables that are only valid for your test process.

https://github.com/mochajs/mocha/issues/185#issuecomment-349700266

This comment on GitHub details on how to do just that.

In your mocha.opts which is referred to in your package.json file for yarn test.

--require test/mocha.env

The above will require a mocha.env file to be sourced before your tests are ran. In mocha.env.ts referenced by the options:

ts process.env.NODE_ENV = 'test';

From here, the NODE_ENV environment variable will be set to test, you can then use the value of this environment variable as a global constant to determine the logic of your application.