Expand and test constant names.

* Purge exec flag from constants.py
* Define the maximum number of contacts per replacement cache.
* Define HEX_NODE_LEN_ID as the length of a node ID in hex.

node/constants.py

@@ -1,13 +1,21 @@
 # ######## KADEMLIA CONSTANTS ###########
 
+BIT_NODE_ID_LEN = 160
+HEX_NODE_ID_LEN = BIT_NODE_ID_LEN // 4
+
 # Small number representing the degree of
 # parallelism in network calls
 alpha = 3
 
 # Maximum number of contacts stored in a bucket
-# NOTE: Should be an even number
+# NOTE: Should be an even number.
 k = 80
 
+# Maximum number of contacts stored in the
+# replacement cache of a bucket
+# NOTE: Should be an even number.
+cache_k = 80
+
 # Timeout for network operations
 # [seconds]
 rpcTimeout = 0.1

test/test_constants.py

@@ -0,0 +1,34 @@
+import unittest
+
+from node import constants
+
+
+class TestConstants(unittest.TestCase):
+
+    def test_exported_names(self):
+        self.assertEqual(160, constants.BIT_NODE_ID_LEN)
+        self.assertEqual(
+            constants.BIT_NODE_ID_LEN // 4,
+            constants.HEX_NODE_ID_LEN
+        )
+        self.assertEqual(80, constants.k)
+        self.assertEqual(80, constants.cache_k)
+        self.assertEqual(0.1, constants.rpcTimeout)
+        self.assertEqual(86400, constants.dataExpireTimeout)
+        self.assertEqual(60 * 60 * 1000, constants.refreshTimeout)
+        self.assertEqual(
+            constants.rpcTimeout / 2,
+            constants.iterativeLookupDelay
+        )
+        self.assertEqual(constants.replicateInterval, constants.refreshTimeout)
+        self.assertEqual(
+            constants.refreshTimeout / 5,
+            constants.checkRefreshInterval
+        )
+        self.assertEqual(8192, constants.udpDatagramMaxSize)
+        self.assertEqual("db/ob.db", constants.DB_PATH)
+        self.assertEqual("0.2.1", constants.VERSION)
+
+
+if __name__ == "__main__":
+    unittest.main()