Fix the DST issue

scripts/test/dst.sh

@@ -11,3 +11,4 @@ export PATH="$(yarn bin):$PATH"
 env TZ=America/Sao_Paulo babel-node ./test/dst/parseISO/basic.js
 env TZ=Pacific/Apia babel-node ./test/dst/parseISO/samoa.js
 env TZ=Asia/Damascus babel-node ./test/dst/eachDayOfInterval/basic.js
+env TZ=America/Santiago babel-node ./test/dst/addBusinessDays/basic.js

src/addBusinessDays/index.js

@@ -1,6 +1,6 @@
-import toInteger from '../_lib/toInteger/index.js'
 import isWeekend from '../isWeekend/index.js'
 import toDate from '../toDate/index.js'
+import toInteger from '../_lib/toInteger/index.js'
 
 /**
  * @name addBusinessDays
@@ -32,9 +32,11 @@ export default function addBusinessDays(dirtyDate, dirtyAmount) {
 
   if (isNaN(amount)) return new Date(NaN)
 
+  var hours = date.getHours()
   var numWeekDays = 0
   while (numWeekDays < amount) {
     date.setDate(date.getDate() + 1)
+    date.setHours(hours)
     if (!isWeekend(date)) numWeekDays++
   }
 

test/dst/addBusinessDays/basic.js

@@ -0,0 +1,18 @@
+// This is basic DST test for addBusinessDays
+
+import assert from 'assert'
+import addBusinessDays from '../../../src/addBusinessDays'
+
+if (process.env.TZ !== 'America/Santiago')
+  throw new Error('The test must be run with TZ=America/Santiago')
+
+if (parseInt(process.version.match(/^v(\d+)\./)[1]) < 10)
+  throw new Error('The test must be run on Node.js version >= 10')
+
+console.log(addBusinessDays(new Date(2014, 8 /* Sep */, 1), 10).toString())
+
+assert.deepEqual(
+  // new Date(2014, 8, 7) is the DST day
+  addBusinessDays(new Date(2014, 8 /* Sep */, 1), 10).toString(),
+  'Mon Sep 15 2014 00:00:00 GMT-0300 (Chile Summer Time)'
+)