Add tracetest example for testing instrumentation (#7107)

Fixes https://github.com/open-telemetry/opentelemetry-go/issues/7051

sdk/trace/tracetest/example_test.go

@@ -0,0 +1,37 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package tracetest_test
+
+import (
+	"context"
+	"fmt"
+
+	"go.opentelemetry.io/otel/sdk/trace"
+	"go.opentelemetry.io/otel/sdk/trace/tracetest"
+)
+
+func ExampleSpanRecorder() {
+	ctx := context.Background()
+
+	// Set up an in-memory span recorder and tracer provider.
+	sr := tracetest.NewSpanRecorder()
+	tp := trace.NewTracerProvider(
+		trace.WithSpanProcessor(sr),
+	)
+	defer tp.Shutdown(ctx) //nolint:errcheck // Example code, error handling omitted.
+
+	tracer := tp.Tracer("example/simple")
+
+	// Start and end a span.
+	_, span := tracer.Start(ctx, "test-span")
+	span.End()
+
+	// Print the recorded span name.
+	for _, s := range sr.Ended() {
+		fmt.Println(s.Name())
+	}
+
+	// Output:
+	// test-span
+}