diff --git a/.coveragerc b/.coveragerc
new file mode 100644
index 0000000..74c5a28
--- /dev/null
+++ b/.coveragerc
@@ -0,0 +1,6 @@
+[run]
+omit =
+    pisa/pisad.py
+    pisa/sample_conf.py
+    pisa/time_traveler.py
+    pisa/utils/auth_proxy.py
\ No newline at end of file
diff --git a/pisa/__init__.py b/pisa/__init__.py
index 5d03345..8aa5441 100644
--- a/pisa/__init__.py
+++ b/pisa/__init__.py
@@ -11,8 +11,3 @@ logging.basicConfig(format='%(message)s', level=logging.INFO, handlers=[
     logging.FileHandler(conf.SERVER_LOG_FILE),
     logging.StreamHandler()
 ])
-
-# Create RPC connection with bitcoind
-# TODO: Check if a long lived connection like this may create problems (timeouts)
-bitcoin_cli = AuthServiceProxy("http://%s:%s@%s:%d" % (conf.BTC_RPC_USER, conf.BTC_RPC_PASSWD, conf.BTC_RPC_HOST,
-                                                       conf.BTC_RPC_PORT))
diff --git a/pisa/block_processor.py b/pisa/block_processor.py
index a5f30e3..83b0441 100644
--- a/pisa/block_processor.py
+++ b/pisa/block_processor.py
@@ -1,8 +1,8 @@
 import binascii
 from hashlib import sha256
 
-from pisa import bitcoin_cli
 from pisa.logger import Logger
+from pisa.tools import bitcoin_cli
 from pisa.utils.auth_proxy import JSONRPCException
 
 logger = Logger("BlockProcessor")
@@ -13,7 +13,7 @@ class BlockProcessor:
     def get_block(block_hash):
 
         try:
-            block = bitcoin_cli.getblock(block_hash)
+            block = bitcoin_cli().getblock(block_hash)
 
         except JSONRPCException as e:
             block = None
@@ -25,7 +25,7 @@ class BlockProcessor:
     def get_best_block_hash():
 
         try:
-            block_hash = bitcoin_cli.getbestblockhash()
+            block_hash = bitcoin_cli().getbestblockhash()
 
         except JSONRPCException as e:
             block_hash = None
@@ -37,7 +37,7 @@ class BlockProcessor:
     def get_block_count():
 
         try:
-            block_count = bitcoin_cli.getblockcount()
+            block_count = bitcoin_cli().getblockcount()
 
         except JSONRPCException as e:
             block_count = None
@@ -73,7 +73,7 @@ class BlockProcessor:
                 try:
                     # ToDo: #20-test-tx-decrypting-edge-cases
                     justice_rawtx = appointments[uuid].encrypted_blob.decrypt(dispute_txid)
-                    justice_txid = bitcoin_cli.decoderawtransaction(justice_rawtx).get('txid')
+                    justice_txid = bitcoin_cli().decoderawtransaction(justice_rawtx).get('txid')
                     logger.info("Match found for locator.", locator=locator, uuid=uuid, justice_txid=justice_txid)
 
                 except JSONRPCException as e:
diff --git a/pisa/carrier.py b/pisa/carrier.py
index d4cfbed..130cfca 100644
--- a/pisa/carrier.py
+++ b/pisa/carrier.py
@@ -1,6 +1,6 @@
 from pisa.rpc_errors import *
-from pisa import bitcoin_cli
 from pisa.logger import Logger
+from pisa.tools import bitcoin_cli
 from pisa.utils.auth_proxy import JSONRPCException
 from pisa.errors import UNKNOWN_JSON_RPC_EXCEPTION
 
@@ -20,7 +20,7 @@ class Carrier:
     def send_transaction(self, rawtx, txid):
         try:
             logger.info("Pushing transaction to the network", txid=txid, rawtx=rawtx)
-            bitcoin_cli.sendrawtransaction(rawtx)
+            bitcoin_cli().sendrawtransaction(rawtx)
 
             receipt = Receipt(delivered=True)
 
@@ -70,7 +70,7 @@ class Carrier:
     @staticmethod
     def get_transaction(txid):
         try:
-            tx_info = bitcoin_cli.getrawtransaction(txid, 1)
+            tx_info = bitcoin_cli().getrawtransaction(txid, 1)
 
         except JSONRPCException as e:
             tx_info = None
diff --git a/pisa/inspector.py b/pisa/inspector.py
index 53055b8..1ae4547 100644
--- a/pisa/inspector.py
+++ b/pisa/inspector.py
@@ -2,7 +2,6 @@ import re
 
 from pisa import errors
 import pisa.conf as conf
-from pisa import bitcoin_cli
 from pisa.logger import Logger
 from pisa.appointment import Appointment
 from pisa.block_processor import BlockProcessor
diff --git a/pisa/responder.py b/pisa/responder.py
index 6a1457d..dcce0a6 100644
--- a/pisa/responder.py
+++ b/pisa/responder.py
@@ -1,6 +1,7 @@
+import json
 from queue import Queue
-from threading import Thread
 from hashlib import sha256
+from threading import Thread
 from binascii import unhexlify
 
 from pisa.logger import Logger
@@ -34,6 +35,9 @@ class Job:
 
         return job
 
+    def to_json(self):
+        return json.dumps(self.to_dict())
+
 
 class Responder:
     def __init__(self):
@@ -62,6 +66,8 @@ class Responder:
             # TODO: Add the missing reasons (e.g. RPC_VERIFY_REJECTED)
             pass
 
+        return receipt
+
     def create_job(self, uuid, dispute_txid, justice_txid, justice_rawtx, appointment_end, confirmations=0,
                    retry=False):
 
@@ -155,7 +161,7 @@ class Responder:
 
         for uuid, job in self.jobs.items():
             if job.appointment_end <= height:
-                tx = Carrier.get_transaction(job.dispute_txid)
+                tx = Carrier.get_transaction(job.justice_txid)
 
                 # FIXME: Should be improved with the librarian
                 confirmations = tx.get('confirmations')
diff --git a/pisa/tools.py b/pisa/tools.py
index aeaa310..adba5e5 100644
--- a/pisa/tools.py
+++ b/pisa/tools.py
@@ -1,10 +1,15 @@
 import re
 from http.client import HTTPException
 
-from pisa import bitcoin_cli
+import pisa.conf as conf
 from pisa.logger import Logger
-from pisa.utils.auth_proxy import JSONRPCException
 from pisa.rpc_errors import RPC_INVALID_ADDRESS_OR_KEY
+from pisa.utils.auth_proxy import AuthServiceProxy, JSONRPCException
+
+
+def bitcoin_cli():
+    return AuthServiceProxy("http://%s:%s@%s:%d" % (conf.BTC_RPC_USER, conf.BTC_RPC_PASSWD, conf.BTC_RPC_HOST,
+                                                    conf.BTC_RPC_PORT))
 
 
 # TODO: currently only used in the Responder; might move there or in the BlockProcessor
@@ -13,7 +18,7 @@ def check_tx_in_chain(tx_id, logger=Logger(), tx_label='Transaction'):
     confirmations = 0
 
     try:
-        tx_info = bitcoin_cli.getrawtransaction(tx_id, 1)
+        tx_info = bitcoin_cli().getrawtransaction(tx_id, 1)
 
         if tx_info.get("confirmations"):
             confirmations = int(tx_info.get("confirmations"))
@@ -38,7 +43,7 @@ def can_connect_to_bitcoind():
     can_connect = True
 
     try:
-        bitcoin_cli.help()
+        bitcoin_cli().help()
     except (ConnectionRefusedError, JSONRPCException, HTTPException):
         can_connect = False
 
@@ -50,7 +55,7 @@ def in_correct_network(network):
     testnet3_genesis_block_hash = "000000000933ea01ad0ee984209779baaec3ced90fa3f408719526f8d77f4943"
     correct_network = False
 
-    genesis_block_hash = bitcoin_cli.getblockhash(0)
+    genesis_block_hash = bitcoin_cli().getblockhash(0)
 
     if network == 'mainnet' and genesis_block_hash == mainnet_genesis_block_hash:
         correct_network = True
@@ -65,3 +70,4 @@ def in_correct_network(network):
 def check_txid_format(txid):
     # TODO: #12-check-txid-regexp
     return isinstance(txid, str) and re.search(r'^[0-9A-Fa-f]{64}$', txid) is not None
+
diff --git a/test/simulator/bitcoin_sim_tests.py b/test/simulator/bitcoin_sim_tests.py
index cb1c5bb..f0eafe5 100644
--- a/test/simulator/bitcoin_sim_tests.py
+++ b/test/simulator/bitcoin_sim_tests.py
@@ -1,107 +1,146 @@
+import re
 import os
+import pytest
+from time import sleep
+from threading import Thread
+
+from test.simulator.transaction import TX
+from test.simulator.bitcoind_sim import run_simulator
 from pisa.utils.auth_proxy import AuthServiceProxy, JSONRPCException
 from pisa.conf import BTC_RPC_USER, BTC_RPC_PASSWD, BTC_RPC_HOST, BTC_RPC_PORT
-from pisa.tools import check_txid_format
+
+MIXED_VALUES = values = [-1, 500, '', '111', [], 1.1, None, '', "a" * 31, "b" * 33, os.urandom(32).hex()]
+
+
+@pytest.fixture(scope='module')
+def run_bitcoind():
+    bitcoind_thread = Thread(target=run_simulator, kwargs={"mode": "event"})
+    bitcoind_thread.daemon = True
+    bitcoind_thread.start()
+
+    # It takes a little bit of time to start the API (otherwise the requests are sent too early and they fail)
+    sleep(0.1)
+
+
+@pytest.fixture(scope="module")
+def genesis_block_hash(run_bitcoind):
+    return bitcoin_cli.getblockhash(0)
+
+
+def check_hash_format(txid):
+    # TODO: #12-check-txid-regexp
+    return isinstance(txid, str) and re.search(r'^[0-9A-Fa-f]{64}$', txid) is not None
 
 
 bitcoin_cli = AuthServiceProxy("http://%s:%s@%s:%d" % (BTC_RPC_USER, BTC_RPC_PASSWD, BTC_RPC_HOST, BTC_RPC_PORT))
 
-# Help should always return 0
-assert(bitcoin_cli.help() == 0)
 
-# getblockhash should return a blockid (which matches the txid format)
-block_hash = bitcoin_cli.getblockhash(0)
-assert(check_txid_format(block_hash))
+def test_help(run_bitcoind):
+    # Help should always return 0
+    assert(bitcoin_cli.help() == 0)
 
-# Check that the values are within range and of the proper format (all should fail)
-values = [-1, 500, None, '', '111', [], 1.1]
-print("getblockhash fails ({}):".format(len(values)))
 
-for v in values:
+# FIXME: Better assert for the exceptions would be nice (check the returned errno is the expected one)
+
+def test_getblockhash(genesis_block_hash):
+    # First block
+    assert(check_hash_format(genesis_block_hash))
+
+    # Check that the values are within range and of the proper format (all should fail)
+    for v in MIXED_VALUES:
+        try:
+            bitcoin_cli.getblockhash(v)
+            assert False
+        except JSONRPCException as e:
+            assert True
+
+
+def test_get_block(genesis_block_hash):
+    # getblock should return a list of transactions and the height
+    block = bitcoin_cli.getblock(genesis_block_hash)
+    assert(isinstance(block.get('tx'), list))
+    assert(len(block.get('tx')) != 0)
+    assert(isinstance(block.get('height'), int))
+
+    # It should fail for wrong data formats and random ids
+    for v in MIXED_VALUES:
+        try:
+            bitcoin_cli.getblock(v)
+            assert False
+        except JSONRPCException as e:
+            assert True
+
+
+def test_decoderawtransaction(genesis_block_hash):
+    # decoderawtransaction should only return if the given transaction matches a txid format
+    block = bitcoin_cli.getblock(genesis_block_hash)
+    coinbase_txid = block.get('tx')[0]
+
+    coinbase_tx = bitcoin_cli.getrawtransaction(coinbase_txid).get("hex")
+    tx = bitcoin_cli.decoderawtransaction(coinbase_tx)
+
+    assert(isinstance(tx, dict))
+    assert(isinstance(tx.get('txid'), str))
+    assert(check_hash_format(tx.get('txid')))
+
+    # Therefore should also work for a random transaction hex in our simulation
+    random_tx = TX.create_dummy_transaction()
+    tx = bitcoin_cli.decoderawtransaction(random_tx)
+    assert(isinstance(tx, dict))
+    assert(isinstance(tx.get('txid'), str))
+    assert(check_hash_format(tx.get('txid')))
+
+    # But it should fail for not proper formatted one
+    for v in MIXED_VALUES:
+        try:
+            bitcoin_cli.decoderawtransaction(v)
+            assert False
+        except JSONRPCException as e:
+            assert True
+
+
+def test_sendrawtransaction(genesis_block_hash):
+    # sendrawtransaction should only allow txids that the simulator has not mined yet
+    bitcoin_cli.sendrawtransaction(TX.create_dummy_transaction())
+
+    # Any data not matching the txid format or that matches with an already mined transaction should fail
     try:
-        block_hash = bitcoin_cli.getblockhash(v)
+        genesis_tx = bitcoin_cli.getblock(genesis_block_hash).get("tx")[0]
+        bitcoin_cli.sendrawtransaction(genesis_tx)
         assert False
+
     except JSONRPCException as e:
-        print('\t{}'.format(e))
+        assert True
 
-# getblock should return a list of transactions and the height
-block = bitcoin_cli.getblock(block_hash)
-assert(isinstance(block.get('tx'), list))
-assert(len(block.get('tx')) != 0)
-assert(isinstance(block.get('height'), int))
+    for v in MIXED_VALUES:
+        try:
+            bitcoin_cli.sendrawtransaction(v)
+            assert False
+        except JSONRPCException as e:
+            assert True
 
-# Some fails
-values += ["a"*64, os.urandom(32).hex()]
-print("\ngetblock fails ({}):".format(len(values)))
 
-for v in values:
-    try:
-        block = bitcoin_cli.getblock(v)
-        assert False
-    except JSONRPCException as e:
-        print('\t{}'.format(e))
+def test_getrawtransaction(genesis_block_hash):
+    # getrawtransaction should work for existing transactions, and fail for non-existing ones
+    genesis_tx = bitcoin_cli.getblock(genesis_block_hash).get("tx")[0]
+    tx = bitcoin_cli.getrawtransaction(genesis_tx)
 
-# decoderawtransaction should only return if the given transaction matches a txid format
-coinbase_tx = block.get('tx')[0]
-tx = bitcoin_cli.decoderawtransaction(coinbase_tx)
-assert(isinstance(tx, dict))
-assert(isinstance(tx.get('txid'), str))
-assert(check_txid_format(tx.get('txid')))
+    assert(isinstance(tx, dict))
+    assert(isinstance(tx.get('confirmations'), int))
 
-# Therefore should also work for a random formatted 32-byte hex in our simulation
-random_tx = os.urandom(32).hex()
-tx = bitcoin_cli.decoderawtransaction(random_tx)
-assert(isinstance(tx, dict))
-assert(isinstance(tx.get('txid'), str))
-assert(check_txid_format(tx.get('txid')))
+    for v in MIXED_VALUES:
+        try:
+            bitcoin_cli.getrawtransaction(v)
+            assert False
+        except JSONRPCException as e:
+            assert True
 
-# But it should fail for not proper formatted one
-values = [1, None, '', "a"*63, "b"*65, [], os.urandom(31).hex()]
-print("\ndecoderawtransaction fails ({}):".format(len(values)))
 
-for v in values:
-    try:
-        block = bitcoin_cli.decoderawtransaction(v)
-        assert False
-    except JSONRPCException as e:
-        print('\t{}'.format(e))
-
-# sendrawtransaction should only allow txids that the simulator has not mined yet
-bitcoin_cli.sendrawtransaction(os.urandom(32).hex())
-
-# Any data not matching the txid format or that matches with an already mined transaction should fail
-values += [coinbase_tx]
-
-print("\nsendrawtransaction fails ({}):".format(len(values)))
-
-for v in values:
-    try:
-        block = bitcoin_cli.sendrawtransaction(v)
-        assert False
-    except JSONRPCException as e:
-        print('\t{}'.format(e))
-
-# getrawtransaction should work for existing transactions, and fail for non-existing ones
-tx = bitcoin_cli.getrawtransaction(coinbase_tx)
-
-assert(isinstance(tx, dict))
-assert(isinstance(tx.get('confirmations'), int))
-
-print("\nsendrawtransaction fails ({}):".format(len(values)))
-
-for v in values:
-    try:
-        block = bitcoin_cli.sendrawtransaction(v)
-        assert False
-    except JSONRPCException as e:
-        print('\t{}'.format(e))
-
-# getblockcount should always return a positive integer
-bc = bitcoin_cli.getblockcount()
-assert (isinstance(bc, int))
-assert (bc >= 0)
-
-print("\nAll tests passed!")
+def test_getblockcount():
+    # getblockcount should always return a positive integer
+    bc = bitcoin_cli.getblockcount()
+    assert (isinstance(bc, int))
+    assert (bc >= 0)
 
 
 
diff --git a/test/simulator/bitcoind_sim.py b/test/simulator/bitcoind_sim.py
index b481b43..4306f13 100644
--- a/test/simulator/bitcoind_sim.py
+++ b/test/simulator/bitcoind_sim.py
@@ -1,26 +1,36 @@
-from pisa.conf import FEED_PROTOCOL, FEED_ADDR, FEED_PORT
-from flask import Flask, request, Response, abort
-from test.simulator.zmq_publisher import ZMQPublisher
-from threading import Thread
-from pisa.rpc_errors import *
-from pisa.tools import check_txid_format
-import logging
-import binascii
-import json
 import os
 import time
+import json
+import logging
+import binascii
+from threading import Thread, Event
+from flask import Flask, request, Response, abort
 
+from pisa.rpc_errors import *
+from test.simulator.utils import sha256d
+from test.simulator.transaction import TX
+from test.simulator.zmq_publisher import ZMQPublisher
+from pisa.conf import FEED_PROTOCOL, FEED_ADDR, FEED_PORT
 
 app = Flask(__name__)
 HOST = 'localhost'
 PORT = '18443'
 
-TIME_BETWEEN_BLOCKS = 10
-
-mempool = []
-mined_transactions = {}
-blocks = {}
 blockchain = []
+blocks = {}
+mined_transactions = {}
+mempool = []
+
+mine_new_block = Event()
+
+        
+@app.route('/generate', methods=['POST'])
+def generate():
+    global mine_new_block
+
+    mine_new_block.set()
+
+    return Response(status=200, mimetype='application/json')
 
 
 @app.route('/', methods=['POST'])
@@ -67,10 +77,12 @@ def process_request():
     no_param_err = {"code": RPC_MISC_ERROR, "message": "JSON value is not a {} as expected"}
 
     if method == "decoderawtransaction":
-        txid = get_param(request_data)
+        rawtx = get_param(request_data)
 
-        if isinstance(txid, str):
-            if check_txid_format(txid):
+        if isinstance(rawtx, str) and len(rawtx) % 2 is 0:
+            txid = sha256d(rawtx)
+
+            if TX.deserialize(rawtx) is not None:
                 response["result"] = {"txid": txid}
 
             else:
@@ -82,12 +94,15 @@ def process_request():
 
     elif method == "sendrawtransaction":
         # TODO: A way of rejecting transactions should be added to test edge cases.
-        txid = get_param(request_data)
+        rawtx = get_param(request_data)
 
-        if isinstance(txid, str):
-            if check_txid_format(txid):
+        if isinstance(rawtx, str) and len(rawtx) % 2 is 0:
+            txid = sha256d(rawtx)
+
+            if TX.deserialize(rawtx) is not None:
                 if txid not in list(mined_transactions.keys()):
-                    mempool.append(txid)
+                    mempool.append(rawtx)
+                    response["result"] = {"txid": txid}
 
                 else:
                     response["error"] = {"code": RPC_VERIFY_ALREADY_IN_CHAIN,
@@ -104,10 +119,10 @@ def process_request():
         txid = get_param(request_data)
 
         if isinstance(txid, str):
-            block = blocks.get(mined_transactions.get(txid))
-
-            if block:
-                response["result"] = {"confirmations": len(blockchain) - block.get('height')}
+            if txid in mined_transactions:
+                block = blocks.get(mined_transactions[txid]["block"])
+                rawtx = mined_transactions[txid].get('tx')
+                response["result"] = {"hex": rawtx, "confirmations": len(blockchain) - block.get('height')}
 
             elif txid in mempool:
                 response["result"] = {"confirmations": 0}
@@ -169,6 +184,7 @@ def get_param(request_data):
     param = None
 
     params = request_data.get("params")
+
     if isinstance(params, list) and len(params) > 0:
         param = params[0]
 
@@ -179,40 +195,57 @@ def load_data():
     pass
 
 
-def simulate_mining():
-    global mempool, mined_transactions, blocks, blockchain
+def simulate_mining(mode, time_between_blocks):
+    global mempool, mined_transactions, blocks, blockchain, mine_new_block
     prev_block_hash = None
 
     mining_simulator = ZMQPublisher(topic=b'hashblock', feed_protocol=FEED_PROTOCOL, feed_addr=FEED_ADDR,
                                     feed_port=FEED_PORT)
 
-    while True:
+    # Set the mining event to initialize the blockchain with a block
+    mine_new_block.set()
+
+    while mine_new_block.wait():
         block_hash = os.urandom(32).hex()
-        coinbase_tx_hash = os.urandom(32).hex()
-        txs_to_mine = [coinbase_tx_hash]
+        coinbase_tx = TX.create_dummy_transaction()
+        coinbase_tx_hash = sha256d(coinbase_tx)
+
+        txs_to_mine = dict({coinbase_tx_hash: coinbase_tx})
 
         if len(mempool) != 0:
             # We'll mine up to 100 txs per block
-            txs_to_mine += mempool[:99]
+            for rawtx in mempool[:99]:
+                txid = sha256d(rawtx)
+                txs_to_mine[txid] = rawtx
+
             mempool = mempool[99:]
 
         # Keep track of the mined transaction (to respond to getrawtransaction)
-        for tx in txs_to_mine:
-            mined_transactions[tx] = block_hash
+        for txid, tx in txs_to_mine.items():
+            mined_transactions[txid] = {"tx": tx, "block": block_hash}
+
+        blocks[block_hash] = {"tx": list(txs_to_mine.keys()), "height": len(blockchain),
+                              "previousblockhash": prev_block_hash}
 
-        blocks[block_hash] = {"tx": txs_to_mine, "height": len(blockchain), "previousblockhash": prev_block_hash}
         mining_simulator.publish_data(binascii.unhexlify(block_hash))
         blockchain.append(block_hash)
         prev_block_hash = block_hash
 
         print("New block mined: {}".format(block_hash))
-        print("\tTransactions: {}".format(txs_to_mine))
+        print("\tTransactions: {}".format(list(txs_to_mine.keys())))
 
-        time.sleep(TIME_BETWEEN_BLOCKS)
+        if mode == 'time':
+            time.sleep(time_between_blocks)
 
+        else:
+            mine_new_block.clear()
+            
 
-def run_simulator():
-    mining_thread = Thread(target=simulate_mining)
+def run_simulator(mode='time', time_between_blocks=5):
+    if mode not in ["time", 'event']:
+        raise ValueError("Node must be time or event")
+
+    mining_thread = Thread(target=simulate_mining, args=[mode, time_between_blocks])
     mining_thread.start()
 
     # Setting Flask log to ERROR only so it does not mess with out logging
diff --git a/test/simulator/transaction.py b/test/simulator/transaction.py
new file mode 100644
index 0000000..be49a79
--- /dev/null
+++ b/test/simulator/transaction.py
@@ -0,0 +1,150 @@
+# Porting some functionality from https://github.com/sr-gi/bitcoin_tools with some modifications <3
+from os import urandom
+
+from test.simulator.utils import *
+
+
+class TX:
+    """ Defines a class TX (transaction) that holds all the modifiable fields of a Bitcoin transaction, such as
+    version, number of inputs, reference to previous transactions, input and output scripts, value, etc.
+    """
+
+    def __init__(self):
+        self.version = None
+        self.inputs = None
+        self.outputs = None
+        self.nLockTime = None
+        self.prev_tx_id = []
+        self.prev_out_index = []
+        self.scriptSig = []
+        self.scriptSig_len = []
+        self.nSequence = []
+        self.value = []
+        self.scriptPubKey = []
+        self.scriptPubKey_len = []
+
+        self.offset = 0
+        self.hex = ""
+
+    @classmethod
+    def deserialize(cls, hex_tx):
+        """ Builds a transaction object from the hexadecimal serialization format of a transaction that
+        could be obtained, for example, from a blockexplorer.
+        :param hex_tx: Hexadecimal serialized transaction.
+        :type hex_tx: hex str
+        :return: The transaction build using the provided hex serialized transaction.
+        :rtype: TX
+        """
+
+        tx = cls()
+        tx.hex = hex_tx
+
+        try:
+            tx.version = int(change_endianness(parse_element(tx, 4)), 16)
+
+            # INPUTS
+            tx.inputs = int(parse_varint(tx), 16)
+
+            for i in range(tx.inputs):
+                tx.prev_tx_id.append(change_endianness(parse_element(tx, 32)))
+                tx.prev_out_index.append(int(change_endianness(parse_element(tx, 4)), 16))
+                # ScriptSig
+                tx.scriptSig_len.append(int(parse_varint(tx), 16))
+                tx.scriptSig.append(parse_element(tx, tx.scriptSig_len[i]))
+                tx.nSequence.append(int(parse_element(tx, 4), 16))
+
+            # OUTPUTS
+            tx.outputs = int(parse_varint(tx), 16)
+
+            for i in range(tx.outputs):
+                tx.value.append(int(change_endianness(parse_element(tx, 8)), 16))
+                # ScriptPubKey
+                tx.scriptPubKey_len.append(int(parse_varint(tx), 16))
+                tx.scriptPubKey.append(parse_element(tx, tx.scriptPubKey_len[i]))
+
+            tx.nLockTime = int(parse_element(tx, 4), 16)
+
+            if tx.offset != len(tx.hex):
+                # There is some error in the serialized transaction passed as input. Transaction can't be built
+                tx = None
+            else:
+                tx.offset = 0
+
+        except ValueError:
+            # If a parsing error occurs, the deserialization stops and None is returned
+            tx = None
+
+        return tx
+
+    def serialize(self, rtype=hex):
+        """ Serialize all the transaction fields arranged in the proper order, resulting in a hexadecimal string
+        ready to be broadcast to the network.
+        :param self: self
+        :type self: TX
+        :param rtype: Whether the serialized transaction is returned as a hex str or a byte array.
+        :type rtype: hex or bool
+        :return: Serialized transaction representation (hexadecimal or bin depending on rtype parameter).
+        :rtype: hex str / bin
+        """
+
+        if rtype not in [hex, bin]:
+            raise Exception("Invalid return type (rtype). It should be either hex or bin.")
+        serialized_tx = change_endianness(int2bytes(self.version, 4))  # 4-byte version number (LE).
+
+        # INPUTS
+        serialized_tx += encode_varint(self.inputs)  # Varint number of inputs.
+
+        for i in range(self.inputs):
+            serialized_tx += change_endianness(self.prev_tx_id[i])  # 32-byte hash of the previous transaction (LE).
+            serialized_tx += change_endianness(int2bytes(self.prev_out_index[i], 4))  # 4-byte output index (LE)
+            serialized_tx += encode_varint(len(self.scriptSig[i]) // 2)  # Varint input script length.
+            # ScriptSig
+            serialized_tx += self.scriptSig[i]  # Input script.
+            serialized_tx += int2bytes(self.nSequence[i], 4)  # 4-byte sequence number.
+
+        # OUTPUTS
+        serialized_tx += encode_varint(self.outputs)  # Varint number of outputs.
+
+        if self.outputs != 0:
+            for i in range(self.outputs):
+                serialized_tx += change_endianness(int2bytes(self.value[i], 8))  # 8-byte field Satoshi value (LE)
+                # ScriptPubKey
+                serialized_tx += encode_varint(len(self.scriptPubKey[i]) // 2)  # Varint Output script length.
+                serialized_tx += self.scriptPubKey[i]  # Output script.
+
+        serialized_tx += int2bytes(self.nLockTime, 4)  # 4-byte lock time field
+
+        # If return type has been set to binary, the serialized transaction is converted.
+        if rtype is bin:
+            serialized_tx = unhexlify(serialized_tx)
+
+        return serialized_tx
+
+    @staticmethod
+    def create_dummy_transaction(prev_tx_id=None, prev_out_index=None):
+        tx = TX()
+
+        if prev_tx_id is None:
+            prev_tx_id = urandom(32).hex()
+
+        if prev_out_index is None:
+            prev_out_index = 0
+
+        tx.version = 1
+        tx.inputs = 1
+        tx.outputs = 1
+        tx.prev_tx_id = [prev_tx_id]
+        tx.prev_out_index = [prev_out_index]
+        tx.nLockTime = 0
+        tx.scriptSig = [
+            '47304402204e45e16932b8af514961a1d3a1a25fdf3f4f7732e9d624c6c61548ab5fb8cd410220181522ec8eca07de4860'
+            'a4acdd12909d831cc56cbbac4622082221a8768d1d0901']
+        tx.scriptSig_len = [77]
+        tx.nSequence = [4294967295]
+        tx.value = [5000000000]
+        tx.scriptPubKey = [
+            '4104ae1a62fe09c5f51b13905f07f06b99a2f7159b2225f374cd378d71302fa28414e7aab37397f554a7df5f142c21c'
+            '1b7303b8a0626f1baded5c72a704f7e6cd84cac']
+        tx.scriptPubKey_len = [67]
+
+        return tx.serialize()
diff --git a/test/simulator/utils.py b/test/simulator/utils.py
new file mode 100644
index 0000000..f2f2883
--- /dev/null
+++ b/test/simulator/utils.py
@@ -0,0 +1,128 @@
+# Porting some functionality from https://github.com/sr-gi/bitcoin_tools with some modifications <3
+from hashlib import sha256
+from binascii import unhexlify
+
+
+def change_endianness(x):
+    """ Changes the endianness (from BE to LE and vice versa) of a given value.
+    :param x: Given value which endianness will be changed.
+    :type x: hex str
+    :return: The opposite endianness representation of the given value.
+    :rtype: hex str
+    """
+
+    # If there is an odd number of elements, we make it even by adding a 0
+    if (len(x) % 2) == 1:
+        x += "0"
+
+    y = bytes(x, 'utf-8')
+    z = y[::-1]
+    return z.decode('utf-8')
+
+
+def parse_varint(tx):
+    """ Parses a given transaction for extracting an encoded varint element.
+    :param tx: Transaction where the element will be extracted.
+    :type tx: TX
+    :return: The b-bytes representation of the given value (a) in hex format.
+    :rtype: hex str
+    """
+
+    # First of all, the offset of the hex transaction if moved to the proper position (i.e where the varint should be
+    #  located) and the length and format of the data to be analyzed is checked.
+    data = tx.hex[tx.offset:]
+    assert (len(data) > 0)
+    size = int(data[:2], 16)
+    assert (size <= 255)
+
+    # Then, the integer is encoded as a varint using the proper prefix, if needed.
+    if size <= 252:  # No prefix
+        storage_length = 1
+    elif size == 253:  # 0xFD
+        storage_length = 3
+    elif size == 254:  # 0xFE
+        storage_length = 5
+    elif size == 255:  # 0xFF
+        storage_length = 9
+    else:
+        raise Exception("Wrong input data size")
+
+    # Finally, the storage length is used to extract the proper number of bytes from the transaction hex and the
+    # transaction offset is updated.
+    varint = data[:storage_length * 2]
+    tx.offset += storage_length * 2
+
+    return varint
+
+
+def parse_element(tx, size):
+    """ Parses a given transaction to extract an element of a given size.
+    :param tx: Transaction where the element will be extracted.
+    :type tx: TX
+    :param size: Size of the parameter to be extracted.
+    :type size: int
+    :return: The extracted element.
+    :rtype: hex str
+    """
+
+    element = tx.hex[tx.offset:tx.offset + size * 2]
+    tx.offset += size * 2
+    return element
+
+
+def encode_varint(value):
+    """ Encodes a given integer value to a varint. It only used the four varint representation cases used by bitcoin:
+    1-byte, 2-byte, 4-byte or 8-byte integers.
+    :param value: The integer value that will be encoded into varint.
+    :type value: int
+    :return: The varint representation of the given integer value.
+    :rtype: str
+    """
+
+    # The value is checked in order to choose the size of its final representation.
+    # 0xFD(253), 0xFE(254) and 0xFF(255) are special cases, since are the prefixes defined for 2-byte, 4-byte
+    # and 8-byte long values respectively.
+    if value < pow(2, 8) - 3:
+        size = 1
+        varint = int2bytes(value, size)  # No prefix
+    else:
+        if value < pow(2, 16):
+            size = 2
+            prefix = 253  # 0xFD
+        elif value < pow(2, 32):
+            size = 4
+            prefix = 254  # 0xFE
+        elif value < pow(2, 64):
+            size = 8
+            prefix = 255  # 0xFF
+        else:
+            raise Exception("Wrong input data size")
+        varint = format(prefix, 'x') + change_endianness(int2bytes(value, size))
+
+    return varint
+
+
+def int2bytes(a, b):
+    """ Converts a given integer value (a) its b-byte representation, in hex format.
+    :param a: Value to be converted.
+    :type a: int
+    :param b: Byte size to be filled.
+    :type b: int
+    :return: The b-bytes representation of the given value (a) in hex format.
+    :rtype: hex str
+    """
+
+    m = pow(2, 8*b) - 1
+    if a > m:
+        raise Exception(str(a) + " is too big to be represented with " + str(b) + " bytes. Maximum value is "
+                        + str(m) + ".")
+
+    return ('%0' + str(2 * b) + 'x') % a
+
+
+def sha256d(hex_data):
+    data = unhexlify(hex_data)
+    double_sha256 = sha256(sha256(data).digest()).hexdigest()
+
+    return change_endianness(double_sha256)
+
diff --git a/test/unit/conftest.py b/test/unit/conftest.py
index ab6af2b..2c0bdea 100644
--- a/test/unit/conftest.py
+++ b/test/unit/conftest.py
@@ -1,14 +1,15 @@
 import pytest
+import requests
 from time import sleep
 from threading import Thread
 
 from pisa.api import start_api
-from test.simulator.bitcoind_sim import run_simulator
+from test.simulator.bitcoind_sim import run_simulator, HOST, PORT
 
 
 @pytest.fixture(scope='session')
 def run_bitcoind():
-    bitcoind_thread = Thread(target=run_simulator)
+    bitcoind_thread = Thread(target=run_simulator, kwargs={"mode": "event"})
     bitcoind_thread.daemon = True
     bitcoind_thread.start()
 
@@ -24,3 +25,10 @@ def run_api():
 
     # It takes a little bit of time to start the API (otherwise the requests are sent too early and they fail)
     sleep(0.1)
+
+
+def generate_block():
+    requests.post(url="http://{}:{}/generate".format(HOST, PORT), timeout=5)
+    sleep(0.5)
+
+
diff --git a/test/unit/test_api.py b/test/unit/test_api.py
index 8a5661d..ba052e5 100644
--- a/test/unit/test_api.py
+++ b/test/unit/test_api.py
@@ -1,37 +1,42 @@
-import os
 import json
 import pytest
-import time
 import requests
 from hashlib import sha256
 from binascii import unhexlify
 
 from apps.cli.blob import Blob
 from pisa import HOST, PORT, logging
+from test.simulator.utils import sha256d
+from test.simulator.transaction import TX
+from test.unit.conftest import generate_block
 from pisa.utils.auth_proxy import AuthServiceProxy
-from test.simulator.bitcoind_sim import TIME_BETWEEN_BLOCKS
 from pisa.conf import BTC_RPC_USER, BTC_RPC_PASSWD, BTC_RPC_HOST, BTC_RPC_PORT, MAX_APPOINTMENTS
 
 logging.getLogger().disabled = True
+
 PISA_API = "http://{}:{}".format(HOST, PORT)
 MULTIPLE_APPOINTMENTS = 10
 
 appointments = []
-locator_dispute_txid_map = {}
+locator_dispute_tx_map = {}
 
 
-def generate_dummy_appointment(dispute_txid):
+def generate_dummy_appointment():
     r = requests.get(url=PISA_API + '/get_block_count', timeout=5)
 
     current_height = r.json().get("block_count")
 
-    dummy_appointment_data = {"tx": os.urandom(32).hex(), "tx_id": dispute_txid, "start_time": current_height + 5,
+    dispute_tx = TX.create_dummy_transaction()
+    dispute_txid = sha256d(dispute_tx)
+    justice_tx = TX.create_dummy_transaction(dispute_txid)
+
+    dummy_appointment_data = {"tx": justice_tx, "tx_id": dispute_txid, "start_time": current_height + 5,
                               "end_time": current_height + 30, "dispute_delta": 20}
 
     cipher = "AES-GCM-128"
     hash_function = "SHA256"
 
-    locator = sha256(unhexlify(dummy_appointment_data.get("tx_id"))).hexdigest()
+    locator = sha256(unhexlify(dispute_txid)).hexdigest()
     blob = Blob(dummy_appointment_data.get("tx"), cipher, hash_function)
 
     encrypted_blob = blob.encrypt((dummy_appointment_data.get("tx_id")))
@@ -41,22 +46,13 @@ def generate_dummy_appointment(dispute_txid):
                    "dispute_delta": dummy_appointment_data.get("dispute_delta"),
                    "encrypted_blob": encrypted_blob, "cipher": cipher, "hash_function": hash_function}
 
-    return appointment
+    return appointment, dispute_tx
 
 
 @pytest.fixture
-def new_appointment(dispute_txid=None):
-    appointment = create_appointment(dispute_txid)
-
-    return appointment
-
-
-def create_appointment(dispute_txid=None):
-    if dispute_txid is None:
-        dispute_txid = os.urandom(32).hex()
-
-    appointment = generate_dummy_appointment(dispute_txid)
-    locator_dispute_txid_map[appointment["locator"]] = dispute_txid
+def new_appointment():
+    appointment, dispute_tx = generate_dummy_appointment()
+    locator_dispute_tx_map[appointment["locator"]] = dispute_tx
 
     return appointment
 
@@ -147,12 +143,12 @@ def test_get_all_appointments_responder():
     bitcoin_cli = AuthServiceProxy("http://%s:%s@%s:%d" % (BTC_RPC_USER, BTC_RPC_PASSWD, BTC_RPC_HOST, BTC_RPC_PORT))
 
     locators = [appointment["locator"] for appointment in appointments]
-    for locator, dispute_txid in locator_dispute_txid_map.items():
+    for locator, dispute_tx in locator_dispute_tx_map.items():
         if locator in locators:
-            bitcoin_cli.sendrawtransaction(dispute_txid)
+            bitcoin_cli.sendrawtransaction(dispute_tx)
 
     # Wait a bit for them to get confirmed
-    time.sleep(TIME_BETWEEN_BLOCKS)
+    generate_block()
 
     # Get all appointments
     r = requests.get(url=PISA_API + "/get_all_appointments")
diff --git a/test/unit/test_carrier.py b/test/unit/test_carrier.py
index 374dd24..d73c749 100644
--- a/test/unit/test_carrier.py
+++ b/test/unit/test_carrier.py
@@ -1,11 +1,13 @@
 import pytest
 import logging
 from os import urandom
-from time import sleep
+
 
 from pisa.carrier import Carrier
+from test.simulator.utils import sha256d
+from test.simulator.transaction import TX
+from test.unit.conftest import generate_block
 from pisa.rpc_errors import RPC_VERIFY_ALREADY_IN_CHAIN, RPC_DESERIALIZATION_ERROR
-from test.simulator.bitcoind_sim import TIME_BETWEEN_BLOCKS
 
 logging.getLogger().disabled = True
 
@@ -24,23 +26,28 @@ def carrier():
 
 def test_send_transaction(run_bitcoind, carrier):
     # We are mocking bitcoind and in our simulator txid == tx
-    tx = urandom(32).hex()
-    receipt = carrier.send_transaction(tx, tx)
+    tx = TX.create_dummy_transaction()
+    txid = sha256d(tx)
+
+    receipt = carrier.send_transaction(tx, txid)
 
     assert(receipt.delivered is True)
 
 
 def test_send_double_spending_transaction(carrier):
     # We can test what happens if the same transaction is sent twice
-    tx = urandom(32).hex()
-    receipt = carrier.send_transaction(tx, tx)
-    sent_txs.append(tx)
+    tx = TX.create_dummy_transaction()
+    txid = sha256d(tx)
+
+    receipt = carrier.send_transaction(tx, txid)
+    sent_txs.append(txid)
 
     # Wait for a block to be mined
-    sleep(2*TIME_BETWEEN_BLOCKS)
+    for _ in range(2):
+        generate_block()
 
     # Try to send it again
-    receipt2 = carrier.send_transaction(tx, tx)
+    receipt2 = carrier.send_transaction(tx, txid)
 
     # The carrier should report delivered True for both, but in the second case the transaction was already delivered
     # (either by himself or someone else)
@@ -51,8 +58,9 @@ def test_send_double_spending_transaction(carrier):
 
 def test_send_transaction_invalid_format(carrier):
     # Test sending a transaction that does not fits the format
-    tx = urandom(31).hex()
-    receipt = carrier.send_transaction(tx, tx)
+    tx = TX.create_dummy_transaction()
+    txid = sha256d(tx)
+    receipt = carrier.send_transaction(txid, txid)
 
     assert (receipt.delivered is False and receipt.reason == RPC_DESERIALIZATION_ERROR)
 
diff --git a/test/unit/test_encrypted_blob.py b/test/unit/test_encrypted_blob.py
index 26e1d9e..25dc78f 100644
--- a/test/unit/test_encrypted_blob.py
+++ b/test/unit/test_encrypted_blob.py
@@ -1,5 +1,4 @@
 from os import urandom
-from cryptography.exceptions import InvalidTag
 
 from pisa import logging
 from pisa.encrypted_blob import EncryptedBlob
diff --git a/test/unit/test_tools.py b/test/unit/test_tools.py
index e3bce92..251663e 100644
--- a/test/unit/test_tools.py
+++ b/test/unit/test_tools.py
@@ -1,4 +1,4 @@
-from pisa import logging, bitcoin_cli
+from pisa import logging
 from pisa.tools import check_txid_format
 from pisa.tools import can_connect_to_bitcoind, in_correct_network
 
diff --git a/test/unit/test_watcher.py b/test/unit/test_watcher.py
index 6d5476b..db19815 100644
--- a/test/unit/test_watcher.py
+++ b/test/unit/test_watcher.py
@@ -1,23 +1,28 @@
 import pytest
 import logging
-from os import urandom
-from time import sleep
 from uuid import uuid4
 from hashlib import sha256
 from threading import Thread
+from binascii import unhexlify
 from queue import Queue, Empty
 
+from apps.cli.blob import Blob
 from pisa.watcher import Watcher
 from pisa.responder import Responder
 from pisa.conf import MAX_APPOINTMENTS
 from pisa.appointment import Appointment
 from pisa.tools import check_txid_format
+from test.simulator.utils import sha256d
+from test.simulator.transaction import TX
+from test.unit.conftest import generate_block
 from pisa.utils.auth_proxy import AuthServiceProxy
-from test.simulator.bitcoind_sim import TIME_BETWEEN_BLOCKS
 from pisa.conf import EXPIRY_DELTA, BTC_RPC_USER, BTC_RPC_PASSWD, BTC_RPC_HOST, BTC_RPC_PORT
 
 logging.getLogger().disabled = True
+
 APPOINTMENTS = 5
+START_TIME_OFFSET = 1
+END_TIME_OFFSET = 1
 
 
 @pytest.fixture(scope="module")
@@ -25,37 +30,44 @@ def watcher():
     return Watcher()
 
 
-def create_appointment(locator=None):
+def generate_dummy_appointment():
     bitcoin_cli = AuthServiceProxy("http://%s:%s@%s:%d" % (BTC_RPC_USER, BTC_RPC_PASSWD, BTC_RPC_HOST, BTC_RPC_PORT))
 
-    if locator is None:
-        locator = urandom(32).hex()
+    dispute_tx = TX.create_dummy_transaction()
+    dispute_txid = sha256d(dispute_tx)
+    justice_tx = TX.create_dummy_transaction(dispute_txid)
 
     start_time = bitcoin_cli.getblockcount() + 1
     end_time = start_time + 1
     dispute_delta = 20
-    encrypted_blob_data = urandom(100).hex()
+
     cipher = "AES-GCM-128"
     hash_function = "SHA256"
 
-    return Appointment(locator, start_time, end_time, dispute_delta, encrypted_blob_data, cipher, hash_function)
+    locator = sha256(unhexlify(dispute_txid)).hexdigest()
+    blob = Blob(justice_tx, cipher, hash_function)
+
+    encrypted_blob = blob.encrypt(dispute_txid)
+
+    appointment = Appointment(locator, start_time, end_time, dispute_delta, encrypted_blob, cipher, hash_function)
+
+    return appointment, dispute_tx
 
 
 def create_appointments(n):
     locator_uuid_map = dict()
     appointments = dict()
-    txids = []
+    dispute_txs = []
 
     for i in range(n):
-        txid = urandom(32)
+        appointment, dispute_tx = generate_dummy_appointment()
         uuid = uuid4().hex
-        locator = sha256(txid).hexdigest()
 
-        appointments[uuid] = create_appointment(locator)
-        locator_uuid_map[locator] = [uuid]
-        txids.append(txid.hex())
+        appointments[uuid] = appointment
+        locator_uuid_map[appointment.locator] = [uuid]
+        dispute_txs.append(dispute_tx)
 
-    return appointments, locator_uuid_map, txids
+    return appointments, locator_uuid_map, dispute_txs
 
 
 def test_init(watcher):
@@ -69,13 +81,14 @@ def test_init(watcher):
 
 
 def test_add_appointment(run_bitcoind, watcher):
-    # The watcher automatically fire do_watch and do_subscribe on adding an appointment if it is asleep (initial state).
+    # The watcher automatically fires do_watch and do_subscribe on adding an appointment if it is asleep (initial state)
     # Avoid this by setting the state to awake.
     watcher.asleep = False
 
     # We should be able to add appointments up to the limit
     for _ in range(10):
-        added_appointment, sig = watcher.add_appointment(create_appointment())
+        appointment, dispute_tx = generate_dummy_appointment()
+        added_appointment, sig = watcher.add_appointment(appointment)
 
         assert added_appointment is True
 
@@ -85,11 +98,13 @@ def test_add_too_many_appointments(watcher):
     watcher.appointments = dict()
 
     for _ in range(MAX_APPOINTMENTS):
-        added_appointment, sig = watcher.add_appointment(create_appointment())
+        appointment, dispute_tx = generate_dummy_appointment()
+        added_appointment, sig = watcher.add_appointment(appointment)
 
         assert added_appointment is True
 
-    added_appointment, sig = watcher.add_appointment(create_appointment())
+    appointment, dispute_tx = generate_dummy_appointment()
+    added_appointment = watcher.add_appointment(appointment)
 
     assert added_appointment is False
 
@@ -102,7 +117,8 @@ def test_do_subscribe(watcher):
     zmq_thread.start()
 
     try:
-        block_hash = watcher.block_queue.get(timeout=MAX_APPOINTMENTS)
+        generate_block()
+        block_hash = watcher.block_queue.get()
         assert check_txid_format(block_hash)
 
     except Empty:
@@ -113,25 +129,28 @@ def test_do_watch(watcher):
     bitcoin_cli = AuthServiceProxy("http://%s:%s@%s:%d" % (BTC_RPC_USER, BTC_RPC_PASSWD, BTC_RPC_HOST, BTC_RPC_PORT))
 
     # We will wipe all the previous data and add 5 appointments
-    watcher.appointments, watcher.locator_uuid_map, txids = create_appointments(APPOINTMENTS)
+    watcher.appointments, watcher.locator_uuid_map, dispute_txs = create_appointments(APPOINTMENTS)
 
     watch_thread = Thread(target=watcher.do_watch)
     watch_thread.daemon = True
     watch_thread.start()
 
     # Broadcast the first two
-    for txid in txids[:2]:
-        bitcoin_cli.sendrawtransaction(txid)
+    for dispute_tx in dispute_txs[:2]:
+        r = bitcoin_cli.sendrawtransaction(dispute_tx)
 
     # After leaving some time for the block to be mined and processed, the number of appointments should have reduced
     # by two
-    sleep(TIME_BETWEEN_BLOCKS*2)
+    for _ in range(START_TIME_OFFSET + END_TIME_OFFSET):
+        generate_block()
+
     assert len(watcher.appointments) == APPOINTMENTS - 2
 
     # The rest of appointments will timeout after the end (2) + EXPIRY_DELTA
     # Wait for an additional block to be safe
 
-    sleep((EXPIRY_DELTA + 2 + 1) * TIME_BETWEEN_BLOCKS)
+    for _ in range(EXPIRY_DELTA + START_TIME_OFFSET + END_TIME_OFFSET):
+        generate_block()
 
     assert len(watcher.appointments) == 0
     assert watcher.asleep is True