implement Executor pattern

internal/executor/local.go

@@ -0,0 +1,16 @@
+package executor
+
+import (
+	"context"
+	"os/exec"
+)
+
+type LocalExecutor struct{}
+
+func (l LocalExecutor) CombinedOutput(ctx context.Context, name string, arg ...string) ([]byte, error) {
+	return l.CommandContext(ctx, name, arg...).CombinedOutput()
+}
+
+func (l LocalExecutor) CommandContext(ctx context.Context, name string, arg ...string) *exec.Cmd {
+	return exec.CommandContext(ctx, name, arg...)
+}