messageID: add NewSafeID testcase

Signed-off-by: Koichi Shiraishi <zchee.io@gmail.com>

messageID_test.go

@@ -4,6 +4,25 @@ import (
 	"testing"
 )
 
+func TestNewSafeID(t *testing.T) {
+	idgen := NewSafeID(1)
+	id1 := idgen.Next()
+	id2 := idgen.Next()
+	if id1 == id2 {
+		t.Fatalf("id1 and id2 are same: id1: %d, id2: %d", id1, id2)
+	}
+
+	idgen = NewSafeID(100)
+	id100 := idgen.Next()
+	id101 := idgen.Next()
+	if id2 == id100 {
+		t.Fatalf("except id2 and id100 not same: id2: %d, id101: %d", id2, id100)
+	}
+	if id100 == id101 {
+		t.Fatalf("id1 and id2 are same: id100: %d, id101: %d", id100, id101)
+	}
+}
+
 var id int
 
 func BenchmarkNewSafeID(b *testing.B) {