spec_test.go: fix tests when run in UTC as local time zone

Providing an offset to time.Parse is not sufficient to have it load the location
information and compute the daylight savings transition, so I added a way to
override the default Location (previously always time.Local).

go.mod

@@ -1 +1,3 @@
 module github.com/robfig/cron/v3
+
+go 1.12

spec_test.go

@@ -1,6 +1,7 @@
 package cron
 
 import (
+	"strings"
 	"testing"
 	"time"
 )
@@ -154,29 +155,29 @@ func TestNext(t *testing.T) {
 		{"2012-11-04T03:00:00-0500", "TZ=America/New_York 0 0 3 * * ?", "2012-11-05T03:00:00-0500"},
 
 		// hourly job
-		{"2012-11-04T00:00:00-0400", "0 0 * * * ?", "2012-11-04T01:00:00-0400"},
-		{"2012-11-04T01:00:00-0400", "0 0 * * * ?", "2012-11-04T01:00:00-0500"},
-		{"2012-11-04T01:00:00-0500", "0 0 * * * ?", "2012-11-04T02:00:00-0500"},
+		{"TZ=America/New_York 2012-11-04T00:00:00-0400", "0 0 * * * ?", "2012-11-04T01:00:00-0400"},
+		{"TZ=America/New_York 2012-11-04T01:00:00-0400", "0 0 * * * ?", "2012-11-04T01:00:00-0500"},
+		{"TZ=America/New_York 2012-11-04T01:00:00-0500", "0 0 * * * ?", "2012-11-04T02:00:00-0500"},
 
 		// 1am nightly job (runs twice)
-		{"2012-11-04T00:00:00-0400", "0 0 1 * * ?", "2012-11-04T01:00:00-0400"},
-		{"2012-11-04T01:00:00-0400", "0 0 1 * * ?", "2012-11-04T01:00:00-0500"},
-		{"2012-11-04T01:00:00-0500", "0 0 1 * * ?", "2012-11-05T01:00:00-0500"},
+		{"TZ=America/New_York 2012-11-04T00:00:00-0400", "0 0 1 * * ?", "2012-11-04T01:00:00-0400"},
+		{"TZ=America/New_York 2012-11-04T01:00:00-0400", "0 0 1 * * ?", "2012-11-04T01:00:00-0500"},
+		{"TZ=America/New_York 2012-11-04T01:00:00-0500", "0 0 1 * * ?", "2012-11-05T01:00:00-0500"},
 
 		// 2am nightly job
-		{"2012-11-04T00:00:00-0400", "0 0 2 * * ?", "2012-11-04T02:00:00-0500"},
-		{"2012-11-04T02:00:00-0500", "0 0 2 * * ?", "2012-11-05T02:00:00-0500"},
+		{"TZ=America/New_York 2012-11-04T00:00:00-0400", "0 0 2 * * ?", "2012-11-04T02:00:00-0500"},
+		{"TZ=America/New_York 2012-11-04T02:00:00-0500", "0 0 2 * * ?", "2012-11-05T02:00:00-0500"},
 
 		// 3am nightly job
-		{"2012-11-04T00:00:00-0400", "0 0 3 * * ?", "2012-11-04T03:00:00-0500"},
-		{"2012-11-04T03:00:00-0500", "0 0 3 * * ?", "2012-11-05T03:00:00-0500"},
+		{"TZ=America/New_York 2012-11-04T00:00:00-0400", "0 0 3 * * ?", "2012-11-04T03:00:00-0500"},
+		{"TZ=America/New_York 2012-11-04T03:00:00-0500", "0 0 3 * * ?", "2012-11-05T03:00:00-0500"},
 
 		// Unsatisfiable
 		{"Mon Jul 9 23:35 2012", "0 0 0 30 Feb ?", ""},
 		{"Mon Jul 9 23:35 2012", "0 0 0 31 Apr ?", ""},
 
 		// Monthly job
-		{"2012-11-04T00:00:00-0400", "0 0 3 3 * ?", "2012-12-03T03:00:00-0500"},
+		{"TZ=America/New_York 2012-11-04T00:00:00-0400", "0 0 3 3 * ?", "2012-12-03T03:00:00-0500"},
 
 		// Test the scenario of DST resulting in midnight not being a valid time.
 		// https://github.com/robfig/cron/issues/157
@@ -218,16 +219,27 @@ func getTime(value string) time.Time {
 		return time.Time{}
 	}
 
+	var location = time.Local
+	if strings.HasPrefix(value, "TZ=") {
+		parts := strings.Fields(value)
+		loc, err := time.LoadLocation(parts[0][len("TZ="):])
+		if err != nil {
+			panic("could not parse location:" + err.Error())
+		}
+		location = loc
+		value = parts[1]
+	}
+
 	var layouts = []string{
 		"Mon Jan 2 15:04 2006",
 		"Mon Jan 2 15:04:05 2006",
 	}
 	for _, layout := range layouts {
-		if t, err := time.ParseInLocation(layout, value, time.Local); err == nil {
+		if t, err := time.ParseInLocation(layout, value, location); err == nil {
 			return t
 		}
 	}
-	if t, err := time.Parse("2006-01-02T15:04:05-0700", value); err == nil {
+	if t, err := time.ParseInLocation("2006-01-02T15:04:05-0700", value, location); err == nil {
 		return t
 	}
 	panic("could not parse time value " + value)