diff --git a/Development/go/testing.md b/Development/go/testing.md
index e65eccf..d425bf1 100644
--- a/Development/go/testing.md
+++ b/Development/go/testing.md
@@ -2,4 +2,84 @@
 
 ## Benchmark
 
-To prevent
+Any benchmark should be careful to prevent **compiler optimization**.
+
+Example `calc.go` in package `calc`:
+
+```go
+package calc
+
+import (
+	"time"
+)
+
+var input float64
+
+func init() {
+	if time.Now().Year() > 1900 {
+		input = 426942694269
+	}
+}
+
+func calc() int {
+	x := input
+	x /= 6.9
+	x /= 4.2
+	x /= 6.9
+	x /= 4.2
+	return int(x)
+}
+```
+
+Example `calc_test.go` in package `calc`:
+
+```go
+package calc
+
+import (
+	"runtime"
+	"testing"
+)
+
+func BenchmarkX(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		calc()
+	}
+}
+
+var sink int
+
+func BenchmarkCalcSink(b *testing.B) {
+	var result int
+	for i := 0; i < b.N; i++ {
+		result = calc()
+	}
+
+	// prevent compiler optimization
+	sink = result
+}
+
+func BenchmarkCalcKeepAlive(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		result := calc()
+
+		// prevent compiler optimization
+		runtime.KeepAlive(result)
+	}
+}
+```
+
+Benchmark result when run with `go test -bench=.`
+
+```txt
+goos: linux
+goarch: amd64
+BenchmarkCalc-4                 1000000000               0.343 ns/op
+BenchmarkCalcSink-4             229652618                5.30 ns/op
+BenchmarkCalcKeepAlive-4        225297381                5.27 ns/op
+```
+
+`BenchmarkCalc` is fast because it has compiler optimization.
+
+There are 2 methods for preventing compiler optimization:
+sink (`BenchmarkCalcSink`) or keep alive (`BenchmarkCalcKeepAlive`).
diff --git a/Extensions/vscode-extensions.md b/Extensions/vscode-extensions.md
index 08083a4..4cb4579 100644
--- a/Extensions/vscode-extensions.md
+++ b/Extensions/vscode-extensions.md
@@ -11,5 +11,3 @@
 [Bracket Pair Colorizer 2](https://github.com/CoenraadS/Bracket-Pair-Colorizer-2)
 
 [Prettier Formatter](https://github.com/prettier/prettier-vscode)
-
-[markdownlint](https://github.com/DavidAnson/vscode-markdownlint)