Add a double spending test program

examples/src/main/java/com/google/bitcoin/examples/DoubleSpend.java

@@ -0,0 +1,47 @@
+package com.google.bitcoin.examples;
+
+import com.google.bitcoin.core.*;
+import com.google.bitcoin.kits.WalletAppKit;
+import com.google.bitcoin.params.RegTestParams;
+import com.google.bitcoin.utils.BriefLogFormatter;
+import com.google.bitcoin.utils.Threading;
+
+import java.io.File;
+import java.math.BigInteger;
+
+/**
+ * This is a little test app that waits for a coin on a local regtest node, then  generates two transactions that double
+ * spend the same output and sends them. It's useful for testing double spend codepaths but is otherwise not something
+ * you would normally want to do.
+ */
+public class DoubleSpend {
+    public static void main(String[] args) throws Exception {
+        BriefLogFormatter.init();
+        final RegTestParams params = RegTestParams.get();
+        WalletAppKit kit = new WalletAppKit(params, new File("."), "doublespend");
+        kit.connectToLocalHost();
+        kit.setAutoSave(false);
+        kit.startAsync();
+        kit.awaitRunning();
+
+        System.out.println(kit.wallet());
+
+        kit.wallet().getBalanceFuture(Utils.COIN, Wallet.BalanceType.AVAILABLE).get();
+        Transaction tx1 = kit.wallet().createSend(new Address(params, "muYPFNCv7KQEG2ZLM7Z3y96kJnNyXJ53wm"), Utils.CENT);
+        Transaction tx2 = kit.wallet().createSend(new Address(params, "muYPFNCv7KQEG2ZLM7Z3y96kJnNyXJ53wm"), Utils.CENT.add(BigInteger.TEN));
+        final Peer peer = kit.peerGroup().getConnectedPeers().get(0);
+        peer.addEventListener(new AbstractPeerEventListener() {
+            @Override
+            public Message onPreMessageReceived(Peer peer, Message m) {
+                System.err.println("Got a message!" + m.getClass().getSimpleName() + ": " + m);
+                return m;
+            }
+        }, Threading.SAME_THREAD);
+        peer.sendMessage(tx1);
+        peer.sendMessage(tx2);
+
+        Thread.sleep(5000);
+        kit.stopAsync();
+        kit.awaitTerminated();
+    }
+}