adding test around adding where clauses

cqlengine/tests/statements/test_base_statement.py

@@ -0,0 +1,11 @@
+from unittest import TestCase
+from cqlengine.statements import BaseCQLStatement, StatementException
+
+
+class BaseStatementTest(TestCase):
+
+    def test_where_clause_type_checking(self):
+        """ tests that only assignment clauses can be added to queries """
+        stmt = BaseCQLStatement('table', [])
+        with self.assertRaises(StatementException):
+            stmt.add_where_clause('x=5')