Make server check that the db object has been wrapped in a serializer

It's only the server that calls it in multiple threads.

nilmdb/server/server.py

@@ -383,6 +383,11 @@ class Server(object):
 
         self.embedded = embedded
         self.db = db
+        if not getattr(db, "_thread_safe", None):
+            raise KeyError("Database object " + str(db) + " doesn't claim "
+                           "to be thread safe.  You should pass "
+                           "nilmdb.utils.serializer_proxy(NilmDB, args) "
+                           "rather than NilmDB(args).")
 
         # Build up global server configuration
         cherrypy.config.update({

tests/test_nilmdb.py

@@ -111,6 +111,11 @@ class TestBlockingServer(object):
         self.db.close()
 
     def test_blocking_server(self):
+        # Server should fail if the database doesn't have a "_thread_safe"
+        # property.
+        with assert_raises(KeyError):
+            nilmdb.Server(object())
+
         # Start web app on a custom port
         self.server = nilmdb.Server(self.db, host = "127.0.0.1",
                                     port = 12380, stoppable = True)