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// @flow
/* eslint-env mocha */
import assert from 'power-assert'
import subMonths from '.'
describe('subMonths', function() {
it('subtracts the given number of months', function() {
const result = subMonths(new Date(2015, 1 /* Feb */, 1), 5)
assert.deepEqual(result, new Date(2014, 8 /* Sep */, 1))
})
it('accepts a timestamp', function() {
const result = subMonths(new Date(2015, 8 /* Sep */, 1).getTime(), 12)
assert.deepEqual(result, new Date(2014, 8 /* Sep */, 1))
})
it('converts a fractional number to an integer', function() {
const result = subMonths(new Date(2015, 1 /* Feb */, 1), 5.999)
assert.deepEqual(result, new Date(2014, 8 /* Sep */, 1))
})
it('implicitly converts number arguments', function() {
// $ExpectedMistake
// @ts-expect-error
const result = subMonths(new Date(2015, 1 /* Feb */, 1), '5')
assert.deepEqual(result, new Date(2014, 8 /* Sep */, 1))
})
it('does not mutate the original date', function() {
const date = new Date(2014, 8 /* Sep */, 1)
subMonths(date, 12)
assert.deepEqual(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 = subMonths(date, 3)
assert.deepEqual(result, new Date(2014, 8 /* Sep */, 30))
})
it('handles dates before 100 AD', function() {
const initialDate = new Date(0)
initialDate.setFullYear(1, 2 /* Mar */, 31)
initialDate.setHours(0, 0, 0, 0)
const expectedResult = new Date(0)
expectedResult.setFullYear(1, 1 /* Feb */, 28)
expectedResult.setHours(0, 0, 0, 0)
const result = subMonths(initialDate, 1)
assert.deepEqual(result, expectedResult)
})
it('returns `Invalid Date` if the given date is invalid', function() {
const result = subMonths(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 = subMonths(new Date(2015, 1 /* Feb */, 1), NaN)
// @ts-expect-error
assert(result instanceof Date && isNaN(result))
})
it('throws TypeError exception if passed less than 2 arguments', function() {
assert.throws(subMonths.bind(null), TypeError)
assert.throws(subMonths.bind(null, 1), TypeError)
})
})
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