Adds basic unit tests for the Carrier

Further testing is required for this one.

test/unit/test_carrier.py

@@ -0,0 +1,81 @@
+import pytest
+from os import urandom
+from time import sleep
+from threading import Thread
+
+from pisa.carrier import Carrier
+from pisa.rpc_errors import RPC_VERIFY_ALREADY_IN_CHAIN, RPC_DESERIALIZATION_ERROR
+from test.simulator.bitcoind_sim import run_simulator, TIME_BETWEEN_BLOCKS
+
+# FIXME: This test do not fully cover the carrier since the simulator does not support every single error bitcoind may
+#        return for RPC_VERIFY_REJECTED and RPC_VERIFY_ERROR. Further development of the simulator / mocks or simulation
+#        with bitcoind is required
+
+
+sent_txs = []
+
+
+@pytest.fixture(autouse=True, scope='session')
+def run_bitcoind():
+    bitcoind_thread = Thread(target=run_simulator)
+    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='session')
+def carrier():
+    return Carrier()
+
+
+def test_send_transaction(carrier):
+    # We are mocking bitcoind and in our simulator txid == tx
+    tx = urandom(32).hex()
+    receipt = carrier.send_transaction(tx, tx)
+
+    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)
+
+    # Wait for a block to be mined
+    sleep(TIME_BETWEEN_BLOCKS)
+
+    # Try to send it again
+    receipt2 = carrier.send_transaction(tx, tx)
+
+    # The carrier should report delivered True for both, but in the second case the transaction was already delivered
+    # (either by himself or someone else)
+    assert(receipt.delivered is True)
+    assert (receipt2.delivered is True and receipt2.confirmations == 1
+            and receipt2.reason == RPC_VERIFY_ALREADY_IN_CHAIN)
+
+
+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)
+
+    assert (receipt.delivered is False and receipt.reason == RPC_DESERIALIZATION_ERROR)
+
+
+def test_get_transaction():
+    # We should be able to get back every transaction we've sent
+    for tx in sent_txs:
+        tx_info = Carrier.get_transaction(tx)
+
+        assert tx_info is not None
+
+
+def test_get_non_existing_transaction():
+    tx_info = Carrier.get_transaction(urandom(32).hex())
+
+    assert tx_info is None
+
+