crypto: Add a way to go from pubkey to route (#2574)

This is intended for use in a future PR for #2414

crypto/encoding/amino/encode_test.go

@@ -8,6 +8,7 @@ import (
 	"github.com/stretchr/testify/require"
 	"github.com/tendermint/tendermint/crypto"
 	"github.com/tendermint/tendermint/crypto/ed25519"
+	"github.com/tendermint/tendermint/crypto/multisig"
 	"github.com/tendermint/tendermint/crypto/secp256k1"
 )
 
@@ -127,3 +128,24 @@ func TestPubKeyInvalidDataProperReturnsEmpty(t *testing.T) {
 	require.NotNil(t, err, "expecting a non-nil error")
 	require.Nil(t, pk, "expecting an empty public key on error")
 }
+
+func TestPubkeyAminoRoute(t *testing.T) {
+	tests := []struct {
+		key     crypto.PubKey
+		want    string
+		wantErr bool
+	}{
+		{ed25519.PubKeyEd25519{}, ed25519.PubKeyAminoRoute, false},
+		{secp256k1.PubKeySecp256k1{}, secp256k1.PubKeyAminoRoute, false},
+		{&multisig.PubKeyMultisigThreshold{}, multisig.PubKeyMultisigThresholdAminoRoute, false},
+	}
+	for i, tc := range tests {
+		got, err := PubkeyAminoRoute(cdc, tc.key)
+		if tc.wantErr {
+			require.Error(t, err, "tc %d", i)
+		} else {
+			require.NoError(t, err, "tc %d", i)
+			require.Equal(t, tc.want, got, "tc %d", i)
+		}
+	}
+}