Why would the preset be required when I've manually added the configuration?

[tim-rohrer]

Here is the jest.config.js file I've been using. It has always required the preset to be included in order to work:

const config = {
  verbose: true,
  extensionsToTreatAsEsm: [".ts"],
  globals: {
    "ts-jest": {
      useESM: true,
    },
  },
  moduleNameMapper: {
    "^(\\.{1,2}/.*)\\.js$": "$1",
  },
  preset: "ts-jest/presets/default-esm",
  rootDir: "src",
  transform: {},
  testEnvironment: "node",
}

If I remove the preset line, I get a bunch of errors when I invoke NODE_OPTIONS=--experimental-vm-modules npx jest using Node 16.

    SyntaxError: Unexpected token ______ (for example, 'export', or ':')

      at Runtime.loadEsmModule (../node_modules/jest-runtime/build/index.js:608:24)
          at async Promise.all (index 0)

I'm pretty certain this problem existed prior to my upgrade to Jest 28 and ts-jest 28.

This is now important because I want to use the preset line my jest-config.js for @shelfio/jest-mongodb.

So why am I required to include the preset in my configuration? I thought it was optional.