Problem: we don't have acceptance tests (#2216)

Solution: have a simple way to start a node and run scripts against it.

acceptance/python/src/test_double_spend.py

@@ -0,0 +1,43 @@
+# # Double Spend testing
+# This test challenge the system with double spends.
+
+import os
+from uuid import uuid4
+from threading import Thread
+import queue
+
+import bigchaindb_driver.exceptions
+from bigchaindb_driver import BigchainDB
+from bigchaindb_driver.crypto import generate_keypair
+
+
+def test_double_create():
+    bdb = BigchainDB(os.environ.get('BIGCHAINDB_ENDPOINT'))
+    alice = generate_keypair()
+
+    results = queue.Queue()
+
+    tx = bdb.transactions.fulfill(
+            bdb.transactions.prepare(
+                operation='CREATE',
+                signers=alice.public_key,
+                asset={'data': {'uuid': str(uuid4())}}),
+            private_keys=alice.private_key)
+
+    def send_and_queue(tx):
+        try:
+            bdb.transactions.send(tx, mode='commit')
+            results.put('OK')
+        except bigchaindb_driver.exceptions.TransportError as e:
+            results.put('FAIL')
+
+    t1 = Thread(target=send_and_queue, args=(tx, ))
+    t2 = Thread(target=send_and_queue, args=(tx, ))
+
+    t1.start()
+    t2.start()
+
+    results = [results.get(timeout=2), results.get(timeout=2)]
+
+    assert results.count('OK') == 1
+    assert results.count('FAIL') == 1