How do you create a test class for a callout in Salesforce?

<pre id="ext-gen27">@isTest
global class MockHttpResponseGenerator implements HttpCalloutMock {
// Implement this interface method
global HTTPResponse respond(HTTPRequest req) {
// Optionally, only send a mock response for a specific endpoint
// and method.
System.assertEquals('http://example.com/example/test', req.getEndpoint());
System.assertEquals('GET', req.getMethod());

// Create a fake response
HttpResponse res = new HttpResponse();
res.setHeader('Content-Type', 'application/json');
res.setBody('{"example":"test"}');
res.setStatusCode(200);
return res;
}
}