Prepare integration test

tests/common.py

@@ -0,0 +1,40 @@
+# local imports
+from chainqueue.cache import Cache
+
+
+class MockCounter:
+
+    def __init__(self):
+        self.c = 0
+
+
+    def next(self):
+        c = self.c
+        self.c += 1
+        return c
+
+
+class MockTokenCache(Cache):
+
+    def __init__(self):
+        self.db = {}
+        self.last_filter = None
+
+    def put(self, chain_spec, cache_tx):
+        self.db[cache_tx.tx_hash] = cache_tx
+
+
+    def get(self, chain_spec, tx_hash):
+        return self.db[tx_hash]
+
+
+    def by_nonce(self, cache_filter):
+        self.last_filter = cache_filter
+
+
+    def by_date(self, cache_filter=None):
+        self.last_filter = cache_filter
+
+
+    def count(self, cache_filter): 
+        self.last_filter = cache_filter