fix: Fix stdouttrace/example_test to make the trace_id same. (#4855)

* fix: Fix stdouttrace/example_test to make the trace_id same.

* fix: restore Example

---------

Co-authored-by: Damien Mathieu <damien.mathieu@elastic.co>

exporters/stdout/stdouttrace/example_test.go

@@ -38,20 +38,20 @@ var tracer = otel.GetTracerProvider().Tracer(
 	trace.WithSchemaURL(semconv.SchemaURL),
 )
 
-func add(ctx context.Context, x, y int64) int64 {
+func add(ctx context.Context, x, y int64) (context.Context, int64) {
 	var span trace.Span
-	_, span = tracer.Start(ctx, "Addition")
+	ctx, span = tracer.Start(ctx, "Addition")
 	defer span.End()
 
-	return x + y
+	return ctx, x + y
 }
 
-func multiply(ctx context.Context, x, y int64) int64 {
+func multiply(ctx context.Context, x, y int64) (context.Context, int64) {
 	var span trace.Span
-	_, span = tracer.Start(ctx, "Multiplication")
+	ctx, span = tracer.Start(ctx, "Multiplication")
 	defer span.End()
 
-	return x * y
+	return ctx, x * y
 }
 
 func Resource() *resource.Resource {
@@ -62,7 +62,7 @@ func Resource() *resource.Resource {
 	)
 }
 
-func InstallExportPipeline(ctx context.Context) (func(context.Context) error, error) {
+func InstallExportPipeline() (func(context.Context) error, error) {
 	exporter, err := stdouttrace.New(stdouttrace.WithPrettyPrint())
 	if err != nil {
 		return nil, fmt.Errorf("creating stdout exporter: %w", err)
@@ -81,7 +81,7 @@ func Example() {
 	ctx := context.Background()
 
 	// Registers a tracer Provider globally.
-	shutdown, err := InstallExportPipeline(ctx)
+	shutdown, err := InstallExportPipeline()
 	if err != nil {
 		log.Fatal(err)
 	}
@@ -91,5 +91,8 @@ func Example() {
 		}
 	}()
 
-	log.Println("the answer is", add(ctx, multiply(ctx, multiply(ctx, 2, 2), 10), 2))
+	ctx, ans := multiply(ctx, 2, 2)
+	ctx, ans = multiply(ctx, ans, 10)
+	ctx, ans = add(ctx, ans, 2)
+	log.Println("the answer is", ans)
 }