test: add responses API test to validate OpenAI Responses functionality

Signed-off-by: Sivanantham Chinnaiyan <[email protected]>

Author: sivanantha321

tests/e2e-aigw/llm_test.go

@@ -13,6 +13,7 @@ import (
 
 	"github.com/openai/openai-go"
 	"github.com/openai/openai-go/option"
+	"github.com/openai/openai-go/responses"
 	"github.com/stretchr/testify/require"
 
 	internaltesting "github.com/envoyproxy/ai-gateway/internal/testing"
@@ -50,6 +51,30 @@ func TestAIGWRun_LLM(t *testing.T) {
 			"chat completion never succeeded")
 	})
 
+	// Responses API (OpenAI Responses)
+	t.Run("responses API", func(t *testing.T) {
+		internaltesting.RequireEventuallyNoError(t, func() error {
+			// POST directly to the Responses endpoint so we don't depend on the
+			// exact client types in the test. The gateway should proxy this to
+			// the backend and return a JSON body.
+			t.Logf("model to use: %q", ollamaModel)
+			client := openai.NewClient(option.WithBaseURL("http://localhost:1975/v1/"))
+			chatReq := responses.ResponseNewParams{
+				Input: responses.ResponseNewParamsInputUnion{OfString: openai.String("Say this is a test")},
+				Model: ollamaModel,
+			}
+			resp, err := client.Responses.New(ctx, chatReq)
+			if err != nil {
+				return fmt.Errorf("responses api failed: %w", err)
+			}
+			if resp.OutputText() != "" {
+				return nil
+			}
+			return fmt.Errorf("empty body from responses API")
+		}, 10*time.Second, 2*time.Second,
+			"responses API never succeeded")
+	})
+
 	t.Run("access metrics", func(t *testing.T) {
 		t.Skip()
 		internaltesting.RequireEventuallyNoError(t, func() error {