Get config from environment or throw error

getEnvConfigOrThrow.js

const getEnvConfigOrThrow = (requiredKeys, env) => {
  const config = requiredKeys.reduce(
    (result, key) => ({
      ...result,
      [key]: env[key],
    }),
    {},
  )

  const missingConfig = Object.entries(config).reduce(
    (missing, [key, value]) => (value ? missing : [...missing, key]),
    [],
  )

  if (missingConfig.length) {
    throw new Error(
      `Missing configuration in environment: ${missingConfig.join(', ')}`,
    )
  }

  return config
}

module.exports = {
  getEnvConfigOrThrow,
}

getEnvConfigOrThrow.spec.js

const {getEnvConfigOrThrow} = require('./getEnvConfigOrThrow')

describe('Get Env Config or Throw', () => {
  it('returns configuration', async () => {
    expect(getEnvConfigOrThrow(['AAA'], {AAA: 1})).toEqual({AAA: 1})
  })

  it('returns only relevant configuration', async () => {
    expect(getEnvConfigOrThrow(['BBB'], {AAA: 1, BBB: 2})).toEqual({BBB: 2})
  })

  it('throws error for missing config', async () => {
    const call = () => getEnvConfigOrThrow(['BBB'], {})
    expect(call).toThrowErrorMatchingInlineSnapshot(
      `"Missing configuration in environment: BBB"`,
    )
  })

  it('throws error for multilpe missing config', async () => {
    const call = () => getEnvConfigOrThrow(['BBB', 'CCC'], {})
    expect(call).toThrowErrorMatchingInlineSnapshot(
      `"Missing configuration in environment: BBB, CCC"`,
    )
  })
})