Added disconnect checks for timeout, unable to read, and unable to write

lib/sqlalchemy/dialects/mssql/pymssql.py

@@ -85,6 +85,9 @@ class MSDialect_pymssql(MSDialect):
 
     def is_disconnect(self, e, connection, cursor):
         for msg in (
+            "Error 20003",  # Connection Timeout
+            "Error 20004",  # Read from SQL server failed
+            "Error 20006",  # Write to SQL Server failed
             "Error 10054",
             "Not connected to any MS SQL server",
             "Connection is closed"

test/dialect/test_mssql.py

@@ -1320,6 +1320,12 @@ class ParseConnectTest(fixtures.TestBase, AssertsCompiledSQL):
                     'user': 'scott', 'database': 'test'}], connection
         )
 
+    def test_pymssql_disconnect(self):
+        dialect = pymssql.dialect()
+
+        for error in ['20003', '20003', '20006']:
+            eq_(dialect.is_disconnect('Error %s' % error, None, None), True)
+
     @testing.only_on(['mssql+pyodbc', 'mssql+pymssql'], "FreeTDS specific test")
     def test_bad_freetds_warning(self):
         engine = engines.testing_engine()