message: 100% code coverage for formatRFC3339
diff: /* eslint-env mocha */
  import assert from 'assert'
  +import sinon from 'sinon'
  import formatRFC3339 from '.'
  import toInteger from '../_lib/toInteger/index'
  import addLeadingZeros from '../_lib/addLeadingZeros/index'
  @@ -29,6 +30,16 @@ describe('formatRFC3339', () => {
  it('formats RFC-3339 date string', () => {
  const date = new Date(2019, 2 /* Mar */, 3, 19, 0, 52, 123)
  assert(formatRFC3339(date) === `2019-03-03T19:00:52${generateOffset(date)}`)
  +
  + var getTimezoneOffsetStub = sinon.stub(Date.prototype, 'getTimezoneOffset')
  +
  + getTimezoneOffsetStub.returns(0)
  + assert(formatRFC3339(date) === '2019-03-03T19:00:52Z')
  +
  + getTimezoneOffsetStub.returns(480)
  + assert(formatRFC3339(date) === '2019-03-03T19:00:52-08:00')
  +
  + getTimezoneOffsetStub.restore()
  })
  it('accepts a timestamp', function () {
  @@ -57,7 +68,7 @@ describe('formatRFC3339', () => {
  const date = new Date(2019, 2 /* Mar */, 3, 19, 0, 52, 123)
  const result = formatRFC3339(date, {
  // @ts-expect-error
  - fractionDigits: '2'
  + fractionDigits: '2',
  })
  assert.equal(result, `2019-03-03T19:00:52.12${generateOffset(date)}`)
  })
  @@ -65,7 +76,7 @@ describe('formatRFC3339', () => {
  it('throws `RangeError` if `options.fractionDigits` is not convertable to 0, 1, 2, 3 or undefined', function () {
  // @ts-expect-error
  const block = formatRFC3339.bind(null, new Date(2019, 2 /* Mar */, 3), {
  - fractionDigits: NaN
  + fractionDigits: NaN,
  })
  assert.throws(block, RangeError)
  })
  