added a find metric helper; useful for testing

otmetricreader/find.go

@@ -0,0 +1,55 @@
+package otmetricreader
+
+import (
+	"context"
+	"fmt"
+
+	"go.opentelemetry.io/otel/attribute"
+	otsdkmetric "go.opentelemetry.io/otel/sdk/metric"
+	"go.opentelemetry.io/otel/sdk/metric/metricdata"
+)
+
+// FindVal is a testing utility to find the value of a specific metric
+// collected by the sdk [metric.ManualReader].
+//
+// It searches for a metric matching the provided metricName and [attribute.Set].
+// The type parameter V specifies the expected value type, which must be
+// either int64 or float64.
+//
+// An error is returned if a metric matching the name and attributes is not found,
+// or if the found metric's value type does not match V.
+func FindVal[V int64 | float64](ctx context.Context, r *otsdkmetric.ManualReader, metricName string, kvs attribute.Set) (V, error) {
+	var zv V
+	res := metricdata.ResourceMetrics{}
+	if err := r.Collect(ctx, &res); err != nil {
+		return zv, err
+	}
+
+	for _, sm := range res.ScopeMetrics {
+		for _, m := range sm.Metrics {
+			if m.Name != metricName {
+				continue
+			}
+			switch vs := m.Data.(type) {
+			case metricdata.Gauge[V]:
+				for _, d := range vs.DataPoints {
+					if !kvs.Equals(&d.Attributes) {
+						continue
+					}
+					return d.Value, nil
+				}
+			case metricdata.Sum[V]:
+				for _, d := range vs.DataPoints {
+					if !kvs.Equals(&d.Attributes) {
+						continue
+					}
+					return d.Value, nil
+				}
+			default:
+				// wrong metric-type (or histogram, which we'll have to implement later)
+				continue
+			}
+		}
+	}
+	return zv, fmt.Errorf("metric %s not found", metricName)
+}

otmetricreader/find_test.go

@@ -0,0 +1,50 @@
+package otmetricreader
+
+import (
+	"context"
+	"testing"
+
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/metric"
+	otsdkmetric "go.opentelemetry.io/otel/sdk/metric"
+)
+
+func TestFindMetricVal(t *testing.T) {
+	ctx := context.Background()
+
+	r := otsdkmetric.NewManualReader()
+	mp := otsdkmetric.NewMeterProvider(otsdkmetric.WithReader(r))
+
+	otM := mp.Meter("foobar")
+	attrSet := attribute.NewSet(attribute.String("fizzlebit", "foobar"), attribute.String("ouch", "icky"))
+
+	// read an int64 counter
+	counter, countErr := otM.Int64Counter("a_counter_int")
+	if countErr != nil {
+		t.Fatalf("failed to register counter metric: %s", countErr)
+	}
+	counter.Add(ctx, 2, metric.WithAttributeSet(attrSet))
+
+	counterVal, counterValErr := FindVal[int64](ctx, r, "a_counter_int", attrSet)
+	if counterValErr != nil {
+		t.Errorf("failed to fetch counter metric value: %s", counterValErr)
+	}
+	if counterVal != 2 {
+		t.Errorf("unexpected counter metric value: want %d; got %d", 2, counterVal)
+	}
+
+	// read an int64 gauge
+	gauge, gaugeErr := otM.Int64Gauge("a_gauge_int")
+	if gaugeErr != nil {
+		t.Fatalf("failed to register gauge metric: %s", gaugeErr)
+	}
+	gauge.Record(ctx, 3, metric.WithAttributeSet(attrSet))
+
+	gaugeVal, gaugeValErr := FindVal[int64](ctx, r, "a_gauge_int", attrSet)
+	if gaugeValErr != nil {
+		t.Errorf("failed to fetch gauge metric value: %s", gaugeValErr)
+	}
+	if gaugeVal != 3 {
+		t.Errorf("unexpected gauge metric value: want %d; got %d", 3, gaugeVal)
+	}
+}