Correct (short) week string result when set start of week (#203)

Close #200

outputer.go

@@ -92,6 +92,10 @@ func (c Carbon) ToWeekString(timezone ...string) string {
 // ToShortWeekString outputs a string in short week layout like "Sun", i18n is supported.
 // 输出缩写星期字符串，支持i18n
 func (c Carbon) ToShortWeekString(timezone ...string) string {
+	return c.toWeekString("short_weeks", timezone)
+}
+
+func (c Carbon) toWeekString(resourceKey string, timezone []string) string {
 	if len(timezone) > 0 {
 		c.loc, c.Error = getLocationByTimezone(timezone[0])
 	}
@@ -101,10 +105,10 @@ func (c Carbon) ToShortWeekString(timezone ...string) string {
 	if len(c.lang.resources) == 0 {
 		c.lang.SetLocale(defaultLocale)
 	}
-	if months, ok := c.lang.resources["short_weeks"]; ok {
+	if months, ok := c.lang.resources[resourceKey]; ok {
 		slice := strings.Split(months, "|")
-		if len(slice) == 7 {
-			return slice[c.Week()]
+		if len(slice) == DaysPerWeek {
+			return slice[c.DayOfWeek()%DaysPerWeek]
 		}
 	}
 	return ""

outputer_test.go

@@ -2,10 +2,11 @@ package carbon
 
 import (
 	"fmt"
-	"github.com/stretchr/testify/assert"
 	"strconv"
 	"testing"
 	"time"
+
+	"github.com/stretchr/testify/assert"
 )
 
 func TestCarbon_String(t *testing.T) {
@@ -1789,3 +1790,21 @@ func TestCarbon_ToStdTime(t *testing.T) {
 	actual := Now().ToStdTime().Format(DateTimeLayout)
 	assert.Equal(t, expected, actual)
 }
+
+func TestCarbon_Issue200(t *testing.T) {
+	assert := assert.New(t)
+
+	tests := []struct {
+		input                   Carbon
+		expectedWeekString      string
+		expectedShortWeekString string
+	}{
+		{Now().StartOfWeek(), "Sunday", "Sun"},
+		{Now().SetWeekStartsAt(Monday).StartOfWeek(), "Monday", "Mon"},
+		{Now().SetWeekStartsAt(Wednesday).StartOfWeek(), "Wednesday", "Wed"},
+	}
+	for index, test := range tests {
+		assert.Equal(test.expectedWeekString, test.input.ToWeekString(), "Current test index is "+strconv.Itoa(index))
+		assert.Equal(test.expectedShortWeekString, test.input.ToShortWeekString(), "Current test index is "+strconv.Itoa(index))
+	}
+}