Pushgateway metrics

const client = require('prom-client');
const collectDefaultMetrics = client.collectDefaultMetrics;
const Registry = client.Registry;
const register = new Registry();
collectDefaultMetrics({ register: register, prefix: 'prefix_' }); //ok, but without prefix

const test = new client.Counter({
    name: 'prefix_test',
    help: 'prefix_test',
    registers: [register]
});
register.registerMetric(test);
test.inc(10); //not ok.

let gateway = new client.Pushgateway('http://127.0.0.1:9091', [], register);

gateway.push({ jobName: 'test' }, function (err, resp, body) {});

I am trying to use Pushgateway. Default metrics pushed successfully but without prefix. But my test counter doesn't push to gateway.
Maybe I missed something? Really lacking a full-featured example with Pushgateway

The issue names no files or tests; start with the provided Registry, collectDefaultMetrics, Counter, and Pushgateway.push flow. Compare the default metrics and test counter in the pushed output, then confirm whether the counter is registered and whether prefix handling matches the expected behavior.