Add package: datehelper

Author: hioki-daichi

kadai4/hioki-daichi/datehelper/datehelper.go

@@ -0,0 +1,24 @@
+/*
+Package datehelper is a collection of convenient functions for manipulating dates.
+*/
+package datehelper
+
+import "time"
+
+// for testing
+var nowFunc = time.Now
+var loadLocationFunc = time.LoadLocation
+
+// IsDuringTheNewYear returns whether the current date is the New Year or not.
+func IsDuringTheNewYear() bool {
+	loc, err := loadLocationFunc("Asia/Tokyo")
+	if err != nil {
+		panic(err)
+	}
+
+	_, month, day := nowFunc().In(loc).Date()
+	if month == time.January && (day == 1 || day == 2 || day == 3) {
+		return true
+	}
+	return false
+}

kadai4/hioki-daichi/datehelper/datehelper_test.go

@@ -0,0 +1,61 @@
+package datehelper
+
+import (
+	"regexp"
+	"testing"
+	"time"
+)
+
+func TestDatehelper_IsDuringTheNewYear(t *testing.T) {
+	loc, err := time.LoadLocation("Asia/Tokyo")
+	if err != nil {
+		t.Fatalf("err %s", err)
+	}
+
+	cases := map[string]struct {
+		year     int
+		month    time.Month
+		day      int
+		expected bool
+	}{
+		"2018-12-31": {year: 2018, month: time.December, day: 31, expected: false},
+		"2019-01-01": {year: 2019, month: time.January, day: 1, expected: true},
+		"2019-01-02": {year: 2019, month: time.January, day: 2, expected: true},
+		"2019-01-03": {year: 2019, month: time.January, day: 3, expected: true},
+		"2019-01-04": {year: 2019, month: time.January, day: 4, expected: false},
+	}
+
+	for n, c := range cases {
+		c := c
+		t.Run(n, func(t *testing.T) {
+			nowFunc = func() time.Time {
+				return time.Date(c.year, c.month, c.day, 0, 0, 0, 0, loc)
+			}
+
+			expected := c.expected
+			actual := IsDuringTheNewYear()
+			if actual != expected {
+				t.Errorf(`expected: "%t" actual: "%t"`, expected, actual)
+			}
+		})
+	}
+}
+
+func TestDatehelper_IsDuringTheNewYear_Panic(t *testing.T) {
+	loadLocationFunc = func(name string) (*time.Location, error) {
+		return time.LoadLocation("Nonexistent/Location")
+	}
+
+	defer func() {
+		err := recover()
+		if err == nil {
+			t.Fatal("did not panic")
+		}
+		expected := "cannot find Nonexistent/Location in zip file "
+		actual := err.(error).Error()
+		if !regexp.MustCompile(expected).MatchString(actual) {
+			t.Errorf(`unmatched error: expected: "%s" actual: "%s"`, expected, actual)
+		}
+	}()
+	IsDuringTheNewYear()
+}