如何从Java集成测试修改网络连接？

Question

I've written a Java class ( MyRestClient ) that needs to hit a third-party RESTful API and do some processing with the HTTP response returned from their server. I'm now trying to write a series of successful integration tests (using JUnit as the underlying testng lib) between MyRestClient and the 3rd party API to make sure this class behaves correctly under a variety of circumstances:

• Everything is perfect (RESTful API call was correct and the server returns a meaningful response)
• Bad API call and server returns an application-layer error code
• A variety of non-200 HTTP codes get returned, including 403, 404 and 500
• No network connection
• ...etc.

The 4th item on that list (" No network connection ") is what I'm currently stuck on. I'm using Jersey under the hood to perform my actual REST calls, however Jersey is itself just based on java.net.* . If at all possible, I'd like to "break" Jersey's/Java's ability to fire a network connection while my shouldThrowExceptionOnBadNetworkConnection() test method is executing, and then turn it back "on" so that the next test method can behave normally.

I've been looking at the Charles Proxy which seems to do just this, however there doesn't seem to be a Java library for managing it at runtime.

So I ask: How do I turn Java networking "off" for a specific integration test? Thanks in advance.

Answer 1

Make MyRestClient testable by having it declare a protected method that returns the URL and have it use that instead if a private field.

In your JUnit test, you an anonymous class to override that method do it returns junk:

MyRestClient willFail = new MyRestClient() {
    protected String getUrl() {
        return "http://not.a.real.address";
    }
}

There are also mocking libraries that can do similar things