I found a solution to the problem by omitting JS files in my test folder from being included in the Jest coverage reports. This can be done by setting the collectCoverageFrom configuration property in my jest.config.cjs file:

  collectCoverageFrom: [
    "!./**/*.{js,jsx}", // exclude JS files inside of the unit test folder
  ]

By doing this, I can freely create JS files in my test folder that contain any helper functions I need for my tests.

Coverage collection is performed by Jest in the node context. The helper function setUpTest that I wanted to keep in a separate JS file performs Puppeteer operations that are in the browser context. Because I directly import my helper function into my test files, Jest was trying to collect coverage information from it during my tests and was not able to do so. In this case, Jest uses the variable cov_1kbir0kkub during coverage collection, but it only exists within the node context, not within the browser context when setUpTest is calling functions like page.evaluate. Hence the reference error.