Gateway integration tests allow any protocol level errors such as missing HTTP headers, incorrect SSL handling or request/response body mismatches to be flushed out at the finest testing granularity possible.

Any special case error handling should also be tested to ensure the service and protocol client employed respond as expected in exceptional circumstances.

At times it is difficult to trigger abnormal behaviours such as timeouts or slow responses from the external component. In this case it can be beneficial to use a stub version of the external component as a test harness which can be configured to fail in predetermined ways.

State management can be difficult when testing against external components since the tests will rely on certain data being available. One way to mitigate this problem is to agree on a fixed set of representative but harmless data that is guaranteed to be available in every environment.