rsnext/test/integration/env-config/app/pages/api/all.js

const variables = [
  'PROCESS_ENV_KEY',
  'ENV_FILE_KEY',
  'LOCAL_ENV_FILE_KEY',
  'ENV_FILE_LOCAL_OVERRIDE_TEST',
  'PRODUCTION_ENV_FILE_KEY',
  'LOCAL_PRODUCTION_ENV_FILE_KEY',
  'DEVELOPMENT_ENV_FILE_KEY',
  'LOCAL_DEVELOPMENT_ENV_FILE_KEY',
  'ENV_FILE_DEVELOPMENT_OVERRIDE_TEST',
  'ENV_FILE_DEVELOPMENT_LOCAL_OVERRIDEOVERRIDE_TEST',
  'ENV_FILE_PRODUCTION_OVERRIDEOVERRIDE_TEST',
  'ENV_FILE_PRODUCTION_LOCAL_OVERRIDEOVERRIDE_TEST',
  'TEST_ENV_FILE_KEY',
  'LOCAL_TEST_ENV_FILE_KEY',
  'ENV_FILE_TEST_OVERRIDE_TEST',
  'ENV_FILE_TEST_LOCAL_OVERRIDEOVERRIDE_TEST',
  'ENV_FILE_EXPANDED',
  'ENV_FILE_EXPANDED_CONCAT',
  'ENV_FILE_EXPANDED_ESCAPED',
]

const items = {}

variables.forEach((variable) => {
  items[variable] = process.env[variable]
})

export default async (req, res) => {
  // Only for testing, don't do this...
  res.json(items)
}