fix tests for non China based people (#269)

- **tests: Playing with Carbon Default is dangerous.**
- **ci: tests were written by someone in PRC timezone**

Fixes #268

.github/workflows/test.yml

@@ -2,8 +2,6 @@ name: test
 
 on:
   push
-env:
-  TZ: "PRC"
 jobs:
 
   test:

database_unit_test.go

@@ -915,6 +915,8 @@ func TestCarbon_Issue240(t *testing.T) {
 
 // https://github.com/dromara/carbon/issues/243
 func TestCarbon_Issue243(t *testing.T) {
+	prepareTest(t)
+
 	SetDefault(Default{
 		Layout:       DateTimeLayout,
 		Timezone:     PRC,

default_bench_test.go

@@ -3,6 +3,8 @@ package carbon
 import "testing"
 
 func BenchmarkCarbon_SetDefault(b *testing.B) {
+	prepareTest(b)
+
 	d := Default{
 		Layout:       DateTimeLayout,
 		Timezone:     Local,

default_unit_test.go

@@ -7,6 +7,8 @@ import (
 )
 
 func TestCarbon_SetDefault(t *testing.T) {
+	prepareTest(t)
+
 	SetDefault(Default{
 		Layout:       DateTimeLayout,
 		Timezone:     PRC,

test.go

@@ -1,5 +1,10 @@
 package carbon
 
+import (
+	"os"
+	"testing"
+)
+
 // SetTestNow sets a test Carbon instance (real or mock) to be returned when a "now" instance is created.
 // 设置当前测试时间
 func (c *Carbon) SetTestNow(carbon Carbon) {
@@ -17,3 +22,31 @@ func (c *Carbon) UnSetTestNow() {
 func (c Carbon) IsSetTestNow() bool {
 	return c.testNow > 0
 }
+
+// TestMain sets up the testing environment for all tests
+// https://pkg.go.dev/testing#hdr-Main
+func TestMain(m *testing.M) {
+	// The whole tests were written for PRC timezone (China).
+	// The codebase of test is too large to be changed.
+	// Without this hack the tests will fail if you use a different timezone than PRC
+	// This will affect the way Go compute the timezone when using time.Local
+	_ = os.Setenv("TZ", "PRC")
+
+	m.Run()
+}
+
+func prepareTest(tb testing.TB) {
+	tb.Helper()
+
+	// Store the current default
+	savedDefault := Default{
+		Layout:       defaultLayout,
+		Timezone:     defaultTimezone,
+		Locale:       defaultLocale,
+		WeekStartsAt: defaultWeekStartsAt,
+	}
+	tb.Cleanup(func() {
+		// restore the default when test is done
+		SetDefault(savedDefault)
+	})
+}