metrics testing: add type aliases to avoid direct prometheus imports

In tests it is sometimes unavoidable to use the Prometheus types directly,
for example when writing a custom gatherer which needs to normalize data
before testing it. device_taint_eviction_test.go does this to strip
out unpredictable data in a histogram.

With type aliases in a package that is explicitly meant for tests we
can avoid adding exceptions for such tests to the global exception list.

Kubernetes-commit: 9f161590bee774e9aefb0ca89442fe9993cbee87

Author: pohly

metrics/testutil/testutil.go

@@ -20,7 +20,9 @@ import (
 	"fmt"
 	"io"
 
+	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/testutil"
+	dto "github.com/prometheus/client_model/go"
 
 	apimachineryversion "k8s.io/apimachinery/pkg/version"
 	"k8s.io/component-base/metrics"
@@ -33,6 +35,14 @@ type TB interface {
 	Fatalf(format string, args ...any)
 }
 
+// MetricFamily is a type alias which enables writing gatherers in tests
+// without importing prometheus directly (https://github.com/kubernetes/kubernetes/issues/99876).
+type MetricFamily = dto.MetricFamily
+
+// GathererFunc is a type alias which enables writing gatherers as a function in tests
+// without importing prometheus directly (https://github.com/kubernetes/kubernetes/issues/99876).
+type GathererFunc = prometheus.GathererFunc
+
 // CollectAndCompare registers the provided Collector with a newly created
 // pedantic Registry. It then does the same as GatherAndCompare, gathering the
 // metrics from the pedantic Registry.