Test the number of replies matches the number of nonces.

If CreateReplies returns too few replies, the test would still pass.

Change-Id: I7a3c7781d0dd17fa8f2b688daea3c40e25175e98

go/protocol/protocol_test.go

diff --git a/go/protocol/protocol_test.go b/go/protocol/protocol_test.go
index c6a9c50..3c1e9e4 100644
--- a/go/protocol/protocol_test.go
+++ b/go/protocol/protocol_test.go
@@ -110,6 +110,10 @@
 			t.Fatal(err)
 		}
 
+		if len(replies) != len(nonces) {
+			t.Fatalf("received %d replies for %d nonces", len(replies), len(nonces))
+		}
+
 		for i, reply := range replies {
 			midpoint, radius, err := VerifyReply(reply, rootPublicKey, nonces[i])
 			if err != nil {