Add benchmark

Author: korthaj

mst_test.go

@@ -36,8 +36,8 @@ func BenchmarkMST(b *testing.B) {
 	n := 1000
 	b.StopTimer()
 	g := New(n)
-	for i := 0; i < n; i++ {
-		g.AddBoth(rand.Intn(n), rand.Intn(n))
+	for i := 0; i < 2*n; i++ {
+		g.AddCost(rand.Intn(n), rand.Intn(n), int64(rand.Int()))
 	}
 	b.StartTimer()
 	for i := 0; i < b.N; i++ {