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// @flow
/* eslint-env mocha */
import assert from 'assert'
import addMonths from '.'
import { getDstTransitions } from '../../test/dst/tzOffsetTransitions'
describe('addMonths', function() {
it('adds the given number of months', function() {
const result = addMonths(new Date(2014, 8 /* Sep */, 1), 5)
assert.deepStrictEqual(result, new Date(2015, 1 /* Feb */, 1))
})
it('accepts a timestamp', function() {
const result = addMonths(new Date(2014, 8 /* Sep */, 1).getTime(), 12)
assert.deepStrictEqual(result, new Date(2015, 8 /* Sep */, 1))
})
it('converts a fractional number to an integer', function() {
const result = addMonths(new Date(2014, 8 /* Sep */, 1), 5.75)
assert.deepStrictEqual(result, new Date(2015, 1 /* Feb */, 1))
})
it('implicitly converts number arguments', function() {
// @ts-expect-error
const result = addMonths(new Date(2014, 8 /* Sep */, 1), '5')
assert.deepStrictEqual(result, new Date(2015, 1 /* Feb */, 1))
})
it('does not mutate the original date', function() {
const date = new Date(2014, 8 /* Sep */, 1)
addMonths(date, 12)
assert.deepStrictEqual(date, new Date(2014, 8 /* Sep */, 1))
})
it('works well if the desired month has fewer days and the provided date is in the last day of a month', function() {
const date = new Date(2014, 11 /* Dec */, 31)
const result = addMonths(date, 2)
assert.deepStrictEqual(result, new Date(2015, 1 /* Feb */, 28))
})
it('handles dates before 100 AD', function() {
const initialDate = new Date(0)
initialDate.setFullYear(0, 0 /* Jan */, 31)
initialDate.setHours(0, 0, 0, 0)
const expectedResult = new Date(0)
expectedResult.setFullYear(0, 1 /* Feb */, 29)
expectedResult.setHours(0, 0, 0, 0)
const result = addMonths(initialDate, 1)
assert.deepStrictEqual(result, expectedResult)
})
it('returns `Invalid Date` if the given date is invalid', function() {
const result = addMonths(new Date(NaN), 5)
// @ts-expect-error
assert(result instanceof Date && isNaN(result))
})
it('returns `Invalid Date` if the given amount is NaN', function() {
const result = addMonths(new Date(2014, 8 /* Sep */, 1), NaN)
// @ts-expect-error
assert(result instanceof Date && isNaN(result))
})
it('throws TypeError exception if passed less than 2 arguments', function() {
// @ts-expect-error
assert.throws(addMonths.bind(null), TypeError)
// @ts-expect-error
assert.throws(addMonths.bind(null, 1), TypeError)
})
const dstTransitions = getDstTransitions(2017)
const dstOnly = dstTransitions.start && dstTransitions.end ? it : it.skip
const tz = Intl.DateTimeFormat().resolvedOptions().timeZone || process.env.tz
const HOUR = 1000 * 60 * 60
const override = (
base: Date,
year = base.getFullYear(),
month = base.getMonth(),
day = base.getDate(),
hour = base.getHours(),
minute = base.getMinutes()
) => new Date(year, month, day, hour, minute)
dstOnly(
`works at DST-start boundary in local timezone: ${tz || '(unknown)'}`,
function() {
const date = dstTransitions.start
const result = addMonths(date!, 2)
assert.deepStrictEqual(
result,
override(date!, date!.getFullYear(), date!.getMonth() + 2)
)
}
)
dstOnly(
`works at DST-start - 30 mins in local timezone: ${tz || '(unknown)'}`,
function() {
const date = new Date(dstTransitions.start!.getTime() - 0.5 * HOUR)
const result = addMonths(date, 2)
const expected = override(date, date.getFullYear(), date.getMonth() + 2)
assert.deepStrictEqual(result, expected)
}
)
dstOnly(
`works at DST-start - 60 mins in local timezone: ${tz || '(unknown)'}`,
function() {
const date = new Date(dstTransitions.start!.getTime() - 1 * HOUR)
const result = addMonths(date, 2)
const expected = override(date, date.getFullYear(), date.getMonth() + 2)
assert.deepStrictEqual(result, expected)
}
)
dstOnly(
`works at DST-end boundary in local timezone: ${tz || '(unknown)'}`,
function() {
const date = dstTransitions.end
const result = addMonths(date!, 2)
assert.deepStrictEqual(
result,
override(
date!,
date!.getFullYear() + (date!.getMonth() >= 10 ? 1 : 0),
(date!.getMonth() + 2) % 12 // protect against wrap for Nov.
)
)
}
)
dstOnly(
`works at DST-end - 30 mins in local timezone: ${tz || '(unknown)'}`,
function() {
const date = new Date(dstTransitions.end!.getTime() - 0.5 * HOUR)
const result = addMonths(date, 2)
assert.deepStrictEqual(
result,
override(
date,
date.getFullYear() + (date.getMonth() >= 10 ? 1 : 0),
(date.getMonth() + 2) % 12 // protect against wrap for Nov.
)
)
}
)
dstOnly(
`works at DST-end - 60 mins in local timezone: ${tz || '(unknown)'}`,
function() {
const date = new Date(dstTransitions.end!.getTime() - 1 * HOUR)
const result = addMonths(date, 2)
assert.deepStrictEqual(
result,
override(
date,
date.getFullYear() + (date.getMonth() >= 10 ? 1 : 0),
(date.getMonth() + 2) % 12 // protect against wrap for Nov.
)
)
}
)
dstOnly(
`doesn't mutate if zero increment is used: ${tz || '(unknown)'}`,
function() {
const date = new Date(dstTransitions.end!)
const result = addMonths(date, 0)
assert.deepStrictEqual(result, date)
}
)
})
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