Throw on an attempt to submit the same transaction twice

Author: mainnet-pat

packages/cashscript/src/network/MockNetworkProvider.ts

@@ -45,6 +45,11 @@ export default class MockNetworkProvider implements NetworkProvider {
     const transactionBin = hexToBin(txHex);
 
     const txid = binToHex(sha256(sha256(transactionBin)).reverse());
+
+    if (this.transactionMap[txid]) {
+      throw new Error(`Transaction with txid ${txid} was already submitted: txn-mempool-conflict`);
+    }
+
     this.transactionMap[txid] = txHex;
 
     const decoded = decodeTransaction(transactionBin);