cli: add description to vote command on how to unvote

cli/candidate_test.go

@@ -41,7 +41,7 @@ func TestRegisterCandidate(t *testing.T) {
 	require.Equal(t, validatorPriv.PublicKey(), vs[0].Key)
 	require.Equal(t, big.NewInt(0), vs[0].Votes)
 
-	t.Run("Vote", func(t *testing.T) {
+	t.Run("VoteUnvote", func(t *testing.T) {
 		e.In.WriteString("one\r")
 		e.Run(t, "neo-go", "wallet", "candidate", "vote",
 			"--rpc-endpoint", "http://"+e.RPC.Addr,
@@ -55,6 +55,19 @@ func TestRegisterCandidate(t *testing.T) {
 		require.Equal(t, validatorPriv.PublicKey(), vs[0].Key)
 		b, _ := e.Chain.GetGoverningTokenBalance(validatorPriv.GetScriptHash())
 		require.Equal(t, b, vs[0].Votes)
+
+		// unvote
+		e.In.WriteString("one\r")
+		e.Run(t, "neo-go", "wallet", "candidate", "vote",
+			"--rpc-endpoint", "http://"+e.RPC.Addr,
+			"--wallet", validatorWallet,
+			"--address", validatorPriv.Address())
+		e.checkTxPersisted(t)
+
+		vs, err = e.Chain.GetEnrollments()
+		require.Equal(t, 1, len(vs))
+		require.Equal(t, validatorPriv.PublicKey(), vs[0].Key)
+		require.Equal(t, big.NewInt(0), vs[0].Votes)
 	})
 
 	// missing address

cli/wallet/validator.go

@@ -53,7 +53,10 @@ func newValidatorCommands() []cli.Command {
 		{
 			Name:      "vote",
 			Usage:     "vote for a validator",
-			UsageText: "vote -w <path> -r <rpc> [-s <timeout>] [-g gas] -a <addr> -c <public key>",
+			UsageText: "vote -w <path> -r <rpc> [-s <timeout>] [-g gas] -a <addr> [-c <public key>]",
+			Description: `Votes for a validator by calling "vote" method of a NEO native
+   contract. Do not provide candidate argument to perform unvoting.
+`,
 			Action: handleVote,
 			Flags: append([]cli.Flag{
 				walletPathFlag,