Suppress AlreadyRegisteredError to fix test retries

lib/telemetry.go

@@ -14,6 +14,7 @@ import (
 	"github.com/armon/go-metrics/prometheus"
 	"github.com/hashicorp/go-hclog"
 	"github.com/hashicorp/go-multierror"
+	prometheuscore "github.com/prometheus/client_golang/prometheus"
 
 	"github.com/hashicorp/consul/lib/retry"
 )
@@ -258,7 +259,7 @@ func dogstatdSink(cfg TelemetryConfig, hostname string) (metrics.MetricSink, err
 	return sink, nil
 }
 
-func prometheusSink(cfg TelemetryConfig, hostname string) (metrics.MetricSink, error) {
+func prometheusSink(cfg TelemetryConfig, _ string) (metrics.MetricSink, error) {
 
 	if cfg.PrometheusOpts.Expiration.Nanoseconds() < 1 {
 		return nil, nil
@@ -266,12 +267,19 @@ func prometheusSink(cfg TelemetryConfig, hostname string) (metrics.MetricSink, e
 
 	sink, err := prometheus.NewPrometheusSinkFrom(cfg.PrometheusOpts)
 	if err != nil {
+		// During testing we may try to register the same metrics collector
+		// multiple times in a single run (e.g. a metrics test fails and
+		// we attempt a retry), resulting in an AlreadyRegisteredError.
+		// Suppress this and move on.
+		if errors.As(err, &prometheuscore.AlreadyRegisteredError{}) {
+			return nil, nil
+		}
 		return nil, err
 	}
 	return sink, nil
 }
 
-func circonusSink(cfg TelemetryConfig, hostname string) (metrics.MetricSink, error) {
+func circonusSink(cfg TelemetryConfig, _ string) (metrics.MetricSink, error) {
 	token := cfg.CirconusAPIToken
 	url := cfg.CirconusSubmissionURL
 	if token == "" && url == "" {