feat(UMetrics): export default nodejs metrics

Author: Goodluckhf

src/UMetrics.js

@@ -1,3 +1,4 @@
+import promClient from 'prom-client';
 import MetricRegistry from './MetricRegistry';
 import GaugeMetric from './metric/GaugeMetric';
 import Transport from './transport/Transport';
@@ -56,9 +57,22 @@ class UMetrics {
    * @return UMetrics
    */
   start() {
+    if (this.nodejsMetricsEnabled) {
+      this.enableExportingDefaultMetrics();
+    }
     this.transport.start();
     return this;
   }
+
+  /**
+   * @private
+   */
+  enableExportingDefaultMetrics() {
+    promClient.collectDefaultMetrics({
+      prefix: this.prefix,
+      timeout: this.nodejsMetricsInterval,
+    });
+  }
 }
 
 // Конструкторы метрик, как внешний интерфейс

src/UMetrics.server.test.js

@@ -56,4 +56,34 @@ describe('UMetrics facade', () => {
     });
     expect(uMetrics.nodejsMetricsInterval).to.be.equals(7000);
   });
+
+  it('Should enable default metrics exports if option provided', () => {
+    let calledCount = 0;
+    const uMetrics = new UMetrics(new Transport(), {
+      port: 1111,
+      nodejsMetricsEnabled: true,
+    });
+
+    uMetrics.enableExportingDefaultMetrics = () => {
+      calledCount += 1;
+    };
+
+    uMetrics.start();
+    expect(calledCount).to.be.equals(1);
+  });
+
+  it('Should not enable default metrics exports if option is not provided', () => {
+    let calledCount = 0;
+    const uMetrics = new UMetrics(new Transport(), {
+      port: 1111,
+      nodejsMetricsEnabled: false,
+    });
+
+    uMetrics.enableExportingDefaultMetrics = () => {
+      calledCount += 1;
+    };
+
+    uMetrics.start();
+    expect(calledCount).to.be.equals(0);
+  });
 });