Add registry keyword argument to PrometheusMetricReader

Author: Manvi2402

exporter/opentelemetry-exporter-prometheus/src/opentelemetry/exporter/prometheus/__init__.py

@@ -135,7 +135,7 @@ class PrometheusMetricReader(MetricReader):
     """Prometheus metric exporter for OpenTelemetry."""
 
     def __init__(
-        self, disable_target_info: bool = False, prefix: str = ""
+        self, disable_target_info: bool = False, prefix: str = "", registry=REGISTRY
     ) -> None:
         super().__init__(
             preferred_temporality={
@@ -151,7 +151,8 @@ def __init__(
         self._collector = _CustomCollector(
             disable_target_info=disable_target_info, prefix=prefix
         )
-        REGISTRY.register(self._collector)
+        self._registry = registry
+        self._registry.register(self._collector)
         self._collector._callback = self.collect
         self._prefix = prefix
 
@@ -166,7 +167,7 @@ def _receive_metrics(
         self._collector.add_metrics_data(metrics_data)
 
     def shutdown(self, timeout_millis: float = 30_000, **kwargs) -> None:
-        REGISTRY.unregister(self._collector)
+        self._registry.unregister(self._collector)
 
 
 class _CustomCollector:

exporter/opentelemetry-exporter-prometheus/tests/test_prometheus_exporter.py

@@ -55,6 +55,14 @@ def setUp(self):
             side_effect=self._mock_registry_register,
         )
 
+    def test_custom_registry(self):
+        from prometheus_client import CollectorRegistry
+        custom_registry = CollectorRegistry()
+        reader = PrometheusMetricReader(registry=custom_registry)
+        # global REGISTRY should NOT be used
+        self._mock_registry_register.assert_not_called()
+        reader.shutdown()
+
     def verify_text_format(
         self, metric: Metric, expect_prometheus_text: str, prefix: str = ""
     ) -> None: