Function mergeOptionWithPreset

packages/jest-config/src/normalize.ts:147–159

(
  options: Config.InitialOptions,
  preset: Config.InitialOptions,
  optionName: T,
)

}

const mergeOptionWithPreset = <T extends 'moduleNameMapper' | 'transform'>(
  options: Config.InitialOptions,
  preset: Config.InitialOptions,
  optionName: T,
) => {
  if (options[optionName] && preset[optionName]) {
    options[optionName] = {
      ...options[optionName],
      ...preset[optionName],
      ...options[optionName],
    };
  }
};

const mergeGlobalsWithPreset = (
  options: Config.InitialOptions,