diff --git a/src/c27_benchmark/concat_string_test.go b/src/c27_benchmark/concat_string_test.go
new file mode 100644
index 0000000..c54d2c0
--- /dev/null
+++ b/src/c27_benchmark/concat_string_test.go
@@ -0,0 +1,49 @@
+package benchmark
+
+import (
+	"bytes"
+	"github.com/go-playground/assert/v2"
+	"testing"
+)
+
+func TestConcatStringByAdd(t *testing.T) {
+	elems := []string{"1", "2", "3", "4", "5"}
+	ret := ""
+	for _, elem := range elems {
+		ret += elem
+	}
+	assert.Equal(t, "12345", ret)
+}
+
+func TestConcatStringByBytesBuffer(t *testing.T) {
+	var buf bytes.Buffer
+	elems := []string{"1", "2", "3", "4", "5"}
+	for _, elem := range elems {
+		buf.WriteString(elem)
+	}
+	assert.Equal(t, "12345", buf.String())
+}
+
+func BenchmarkConcatStringByAdd(b *testing.B) {
+	b.ResetTimer()
+	elems := []string{"1", "2", "3", "4", "5"}
+	ret := ""
+	for i := 0; i < b.N; i++ {
+		for _, elem := range elems {
+			ret += elem
+		}
+	}
+	b.StopTimer()
+}
+
+func BenchmarkConcatStringByBytesBuffer(b *testing.B) {
+	b.ResetTimer()
+	elems := []string{"1", "2", "3", "4", "5"}
+	var buf bytes.Buffer
+	for i := 0; i < b.N; i++ {
+		for _, elem := range elems {
+			buf.WriteString(elem)
+		}
+	}
+	b.StopTimer()
+}