how to simulate lack of network connectivity in unit testing

Question

The general question is how to simulate (as part of a JUnit suite of test cases) lack of network connectivity as this is an important consideration in some test

Answer 1

Sniffy allows you to block outgoing network connections in your JUnit tests - it will throw a ConnectException whenever you try to establish a new connection.

@Rule public SniffyRule sniffyRule = new SniffyRule();

@Test
@DisableSockets
public void testDisableSockets() throws IOException {
    try {
        new Socket("google.com", 22);
        fail("Sniffy should have thrown ConnectException");
    } catch (ConnectException e) {
        assertNotNull(e);
    }
}

It also allows you to test how your application behaves with broken connectivity in runtime. Just add -javaagent:sniffy.jar=5559 to your JVM arguments and point your browser to localhost:5559 - it will open a web page with all discovered connections to downstream systems and controls to disable certain connections.

Disclaimer: I'm the author of Sniffy