ristretto255: add Encode test

ristretto255.go

@@ -133,7 +133,7 @@ func mapToPoint(out *edwards25519.ExtendedGroupElement, t *radix51.FieldElement)
 }
 
 // Encode encodes a Ristretto group element to its canonical bytestring.
-func (e *Element) Encode(ee *Element) []byte {
+func (ee *Element) Encode() []byte {
 	tmp := &radix51.FieldElement{}
 
 	// u1 = (z0 + y0) * (z0 - y0)

ristretto255_test.go

@@ -1,6 +1,7 @@
 package ristretto255
 
 import (
+	"bytes"
 	"encoding/hex"
 	"testing"
 
@@ -64,7 +65,6 @@ func TestSqrtRatioM1(t *testing.T) {
 	}
 }
 
-func TestRistrettoBasepointDecode(t *testing.T) {
 var (
 	// The encoding of Ristretto element that can be represented internally by the Curve25519 base point.
 	compressedRistrettoBasepoint, _ = hex.DecodeString("e2f2ae0a6abc4e71a884a961c500515f58e30b6aa582dd8db6a65945e08d2d76")
@@ -78,6 +78,7 @@ func TestRistrettoBasepointDecode(t *testing.T) {
 	}}
 )
 
+func TestRistrettoEncoding(t *testing.T) {
 	decodedBasepoint := &Element{}
 	err := decodedBasepoint.Decode(compressedRistrettoBasepoint)
 	if err != nil {
@@ -87,4 +88,18 @@ func TestRistrettoBasepointDecode(t *testing.T) {
 	if decodedBasepoint.Equal(&ristrettoBasepoint) != 1 {
 		t.Error("decode succeeded, but got wrong point")
 	}
+
+	roundtripBasepoint := decodedBasepoint.Encode()
+	if !bytes.Equal(compressedRistrettoBasepoint, roundtripBasepoint) {
+		t.Error("decode<>encode roundtrip produced different results")
+	}
+
+	encodedBasepoint := ristrettoBasepoint.Encode()
+	if !bytes.Equal(compressedRistrettoBasepoint, encodedBasepoint) {
+		t.Error("point encode produced different results")
+	}
+}
+
+func TestRistrettoRoundtrip(t *testing.T) {
+	// TODO quickcheck
 }