Add clear() method into PrometheusRegistry to unregister all collectors (#1158)

* Add clear() method into PrometheusRegistry to unregister all collectors
Signed-off-by: Petr Holubec <[email protected]>

* format

Signed-off-by: Gregor Zeitlinger <[email protected]>

* test

Signed-off-by: Gregor Zeitlinger <[email protected]>

---------

Signed-off-by: Gregor Zeitlinger <[email protected]>
Co-authored-by: Petr Holubec <[email protected]>

Author: zeitlinger

prometheus-metrics-model/src/main/java/io/prometheus/metrics/model/registry/PrometheusRegistry.java

@@ -56,6 +56,12 @@ public void unregister(MultiCollector collector) {
     }
   }
 
+  public void clear() {
+    collectors.clear();
+    multiCollectors.clear();
+    prometheusNames.clear();
+  }
+
   public MetricSnapshots scrape() {
     return scrape((PrometheusScrapeRequest) null);
   }

prometheus-metrics-model/src/test/java/io/prometheus/metrics/model/registry/PrometheusRegistryTest.java

@@ -145,4 +145,16 @@ public void registerOkMultiCollector() {
     snapshots = registry.scrape();
     assertThat(snapshots.size()).isZero();
   }
+
+  @Test
+  public void clearOk() {
+    PrometheusRegistry registry = new PrometheusRegistry();
+    registry.register(counterA1);
+    registry.register(counterB);
+    registry.register(gaugeA);
+    assertThat(registry.scrape().size()).isEqualTo(3);
+
+    registry.clear();
+    assertThat(registry.scrape().size()).isZero();
+  }
 }