ace conditions with last response', function() {
          expect(echoAjax.lastResponse).to.be.equal(undefined);

          // Resolving the oldest request doesn't update lastResponse.
          respondToEchoRequest(server.requests[0]);
          return requests[0].completes.then(function() {
            expect(echoAjax.lastResponse).to.be.equal(undefined);

            // Resolving the most recent request does!
            respondToEchoRequest(server.requests[2]);
            return requests[2].completes;
