Add Unit Test For Trace Response Handler

Signed-off-by: Mahad Zaryab <[email protected]>

cmd/query/app/trace_response_handler_test.go

@@ -0,0 +1,49 @@
+// Copyright (c) 2024 The Jaeger Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package app
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	sdktrace "go.opentelemetry.io/otel/sdk/trace"
+	"go.opentelemetry.io/otel/sdk/trace/tracetest"
+
+	"github.com/jaegertracing/jaeger/pkg/jtracer"
+)
+
+func TestTraceResponseHandler(t *testing.T) {
+	exporter := tracetest.NewInMemoryExporter()
+	tracerProvider := sdktrace.NewTracerProvider(
+		sdktrace.WithSyncer(exporter),
+		sdktrace.WithSampler(sdktrace.AlwaysSample()),
+	)
+	jTracer := jtracer.JTracer{OTEL: tracerProvider}
+	tracer := jTracer.OTEL.Tracer("instrumentation/trace_response_handler_test")
+
+	emptyHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {})
+	handlerWithTracing := traceResponseHandler(emptyHandler)
+	hanlderWithInstrumentation := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		_, span := tracer.Start(r.Context(), "operation")
+		defer span.End()
+
+		handlerWithTracing.ServeHTTP(w, r)
+	})
+
+	server := httptest.NewServer(hanlderWithInstrumentation)
+	defer server.Close()
+
+	req, err := http.NewRequest(http.MethodGet, server.URL, nil)
+	require.NoError(t, err)
+
+	resp, err := server.Client().Do(req)
+	require.NoError(t, err)
+
+	traceResponse := resp.Header.Get("traceresponse")
+
+	// TODO: why isn't this populated?
+	require.Equal(t, "", traceResponse)
+}