@future
global static void SomeMethodWithACallout(id accountId){
     TestRestClient trc = new TestRestClient();
     id aId;
     try {
          aId = (Id) accountId;
     } catch (Exception e) {
          throw new exception(‘You fail.’);
     }
     Account a = [select id, name, bar from Account where id = :aId];

     //make your callout
     RestClientHTTPMocks fakeResponse =
new RestClientHTTPMocks(200, ‘Success’, ‘Success’,
new Map<String,String>());
     System.AssertNotEquals(fakeResponse, null);
     Test.setMock(HttpCalloutMock.class, fakeResponse);
     System.AssertNotEquals(trc, null);
     String result = trc.get(‘http://www.google.com’);
}
