add benchmark for csv detector allocs

internal/magic/text_csv_test.go

@@ -0,0 +1,20 @@
+package magic
+
+import (
+	"io"
+	"math/rand"
+	"testing"
+)
+
+func BenchmarkCsv(b *testing.B) {
+	r := rand.New(rand.NewSource(0))
+	data := make([]byte, 4096)
+	if _, err := io.ReadFull(r, data); err != io.ErrUnexpectedEOF && err != nil {
+		b.Fatal(err)
+	}
+
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		Csv(data, 0)
+	}
+}