[CHORE] Move testing code to test file (#44579)

In
#44447
we covered more lines of code in our tests, but we did so by adding more
untested code 😅

Since the new fakeMetadataStore is only used for tests, I'm moving it to
a test file

Signed-off-by: Arthur Silva Sens <[email protected]>

Author: ArthurSens

receiver/prometheusreceiver/internal/metadata/fakemetadata.go

@@ -8,8 +8,6 @@ import (
 
 	"github.com/prometheus/common/model"
 	"github.com/prometheus/prometheus/scrape"
-
-	fakemetadata "github.com/open-telemetry/opentelemetry-collector-contrib/receiver/prometheusreceiver/internal/metadata"
 )
 
 func TestMetadataForMetric_Internal(t *testing.T) {
@@ -27,7 +25,7 @@ func TestMetadataForMetric_Internal(t *testing.T) {
 }
 
 func TestMetadataForMetric_ExternalExactHit(t *testing.T) {
-	store := fakemetadata.NewFakeMetadataStore(map[string]scrape.MetricMetadata{
+	store := newFakeMetadataStore(map[string]scrape.MetricMetadata{
 		"http_requests_total": {
 			MetricFamily: "http_requests_total",
 			Type:         model.MetricTypeCounter,
@@ -46,7 +44,7 @@ func TestMetadataForMetric_ExternalExactHit(t *testing.T) {
 
 func TestMetadataForMetric_NormalizedFallback_Gauge(t *testing.T) {
 	// Simulate a merged metric like "histogram_count" where store only knows the base name.
-	store := fakemetadata.NewFakeMetadataStore(map[string]scrape.MetricMetadata{
+	store := newFakeMetadataStore(map[string]scrape.MetricMetadata{
 		"histogram": {
 			MetricFamily: "histogram",
 			Type:         model.MetricTypeGauge,
@@ -68,7 +66,7 @@ func TestMetadataForMetric_NormalizedFallback_Gauge(t *testing.T) {
 
 func TestMetadataForMetric_NormalizedFallback_CounterKeepsOriginal(t *testing.T) {
 	// If normalized metadata type is Counter, resolved should stay the original name.
-	store := fakemetadata.NewFakeMetadataStore(map[string]scrape.MetricMetadata{
+	store := newFakeMetadataStore(map[string]scrape.MetricMetadata{
 		"requests": {
 			MetricFamily: "requests",
 			Type:         model.MetricTypeCounter,
@@ -106,7 +104,7 @@ func TestMetadataForMetric_Unknown(t *testing.T) {
 
 func TestMetadataForMetric_PrefersInternalOverExternal(t *testing.T) {
 	// Ensure internal metric metadata is used even if external store provides a conflicting entry.
-	store := fakemetadata.NewFakeMetadataStore(map[string]scrape.MetricMetadata{
+	store := newFakeMetadataStore(map[string]scrape.MetricMetadata{
 		scrapeUpMetricName: {
 			MetricFamily: "up_external",
 			Type:         model.MetricTypeCounter,
@@ -126,3 +124,40 @@ func TestMetadataForMetric_PrefersInternalOverExternal(t *testing.T) {
 		t.Fatalf("expected family %q from internal map, got %q", scrapeUpMetricName, m.MetricFamily)
 	}
 }
+
+// fakeMetadataStore implements scrape.MetricMetadataStore for tests.
+// It is safe to use from other packages' tests
+type fakeMetadataStore struct {
+	data map[string]scrape.MetricMetadata
+}
+
+// newFakeMetadataStore creates a FakeMetadataStore initialized with the given metadata.
+func newFakeMetadataStore(init map[string]scrape.MetricMetadata) *fakeMetadataStore {
+	// copy defensively to avoid external mutation
+	cp := make(map[string]scrape.MetricMetadata, len(init))
+	for k, v := range init {
+		cp[k] = v
+	}
+	return &fakeMetadataStore{data: cp}
+}
+
+func (f fakeMetadataStore) ListMetadata() []scrape.MetricMetadata {
+	out := make([]scrape.MetricMetadata, 0, len(f.data))
+	for _, m := range f.data {
+		out = append(out, m)
+	}
+	return out
+}
+
+func (f fakeMetadataStore) GetMetadata(name string) (scrape.MetricMetadata, bool) {
+	m, ok := f.data[name]
+	return m, ok
+}
+
+func (f fakeMetadataStore) SizeMetadata() int {
+	return len(f.data)
+}
+
+func (f fakeMetadataStore) LengthMetadata() int {
+	return len(f.data)
+}

receiver/prometheusreceiver/internal/metadata_test.go

@@ -31,7 +31,6 @@ import (
 	"go.uber.org/zap/zaptest/observer"
 
 	"github.com/open-telemetry/opentelemetry-collector-contrib/internal/common/testutil"
-	fakemetadata "github.com/open-telemetry/opentelemetry-collector-contrib/receiver/prometheusreceiver/internal/metadata"
 )
 
 const (
@@ -2227,7 +2226,7 @@ func newObs(t *testing.T) *receiverhelper.ObsReport {
 func TestDetectAndStoreNativeHistogramStaleness_NonHistogramReturnsFalse(t *testing.T) {
 	tr := newTxn(t, true, true)
 	// metadata says "gauge" → should not be considered native histogram staleness
-	tr.mc = fakemetadata.NewFakeMetadataStore(map[string]scrape.MetricMetadata{
+	tr.mc = newFakeMetadataStore(map[string]scrape.MetricMetadata{
 		"foo": {MetricFamily: "foo", Type: model.MetricTypeGauge},
 	})
 
@@ -2241,7 +2240,7 @@ func TestDetectAndStoreNativeHistogramStaleness_NonHistogramReturnsFalse(t *test
 func TestGetOrCreateMetricFamily_DistinctFamiliesForNativeVsClassic(t *testing.T) {
 	tr := newTxn(t, true, true)
 	// Provide metadata so normalization doesn't kick in; name is the same family
-	tr.mc = fakemetadata.NewFakeMetadataStore(map[string]scrape.MetricMetadata{
+	tr.mc = newFakeMetadataStore(map[string]scrape.MetricMetadata{
 		"same_family": {MetricFamily: "same_family", Type: model.MetricTypeHistogram},
 	})
 
@@ -2329,7 +2328,7 @@ func newTxn(t *testing.T, useMetadata, enableNative bool) *transaction {
 	)
 	ctx = scrape.ContextWithTarget(ctx, target)
 	if useMetadata {
-		ctx = scrape.ContextWithMetricMetadataStore(ctx, fakemetadata.NewFakeMetadataStore(map[string]scrape.MetricMetadata{}))
+		ctx = scrape.ContextWithMetricMetadataStore(ctx, newFakeMetadataStore(map[string]scrape.MetricMetadata{}))
 	}
 	sink := &consumertest.MetricsSink{}
 	settings := receivertest.NewNopSettings(receivertest.NopType)