refactor: use mock api answers for tests

PiperOrigin-RevId: 888667558

Author: google-genai-bot

core/src/main/java/com/google/adk/sessions/VertexAiSessionService.java

@@ -135,7 +135,7 @@ private ListSessionsResponse parseListSessionsResponse(
       JsonNode listSessionsResponseMap, String appName, String userId) {
     JsonNode sessionsNode = listSessionsResponseMap.get("sessions");
     if (sessionsNode == null || sessionsNode.isNull() || sessionsNode.isEmpty()) {
-      return ListSessionsResponse.builder().sessions(new ArrayList<>()).build();
+      return ListSessionsResponse.builder().build();
     }
     List<Map<String, Object>> apiSessions =
         objectMapper.convertValue(sessionsNode, new TypeReference<List<Map<String, Object>>>() {});
@@ -174,7 +174,7 @@ public Single<ListEventsResponse> listEvents(String appName, String userId, Stri
   private ListEventsResponse parseListEventsResponse(JsonNode listEventsResponse) {
     JsonNode sessionEventsNode = listEventsResponse.get("sessionEvents");
     if (sessionEventsNode == null || sessionEventsNode.isEmpty()) {
-      return ListEventsResponse.builder().events(new ArrayList<>()).build();
+      return ListEventsResponse.builder().build();
     }
     return ListEventsResponse.builder()
         .events(

core/src/test/java/com/google/adk/sessions/MockApiAnswer.java

@@ -36,14 +36,25 @@ class MockApiAnswer implements Answer<ApiResponse> {
 
   private final Map<String, String> sessionMap;
   private final Map<String, String> eventMap;
+  private final String rawApiResponse;
 
   MockApiAnswer(Map<String, String> sessionMap, Map<String, String> eventMap) {
     this.sessionMap = sessionMap;
     this.eventMap = eventMap;
+    this.rawApiResponse = null;
+  }
+
+  MockApiAnswer(String rawApiResponse) {
+    this.sessionMap = null;
+    this.eventMap = null;
+    this.rawApiResponse = rawApiResponse;
   }
 
   @Override
   public ApiResponse answer(InvocationOnMock invocation) throws Throwable {
+    if (rawApiResponse != null) {
+      return responseWithBody(rawApiResponse);
+    }
     String httpMethod = invocation.getArgument(0);
     String path = invocation.getArgument(1);
     if (httpMethod.equals("POST") && SESSIONS_REGEX.matcher(path).matches()) {

core/src/test/java/com/google/adk/sessions/VertexAiSessionServiceTest.java

@@ -25,8 +25,6 @@
 import java.util.Optional;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
-import okhttp3.MediaType;
-import okhttp3.ResponseBody;
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -39,21 +37,6 @@
 public class VertexAiSessionServiceTest {
 
   private static final ObjectMapper mapper = JsonBaseModel.getMapper();
-  private static final MediaType JSON_MEDIA_TYPE =
-      MediaType.parse("application/json; charset=utf-8");
-
-  private static ApiResponse apiResponseJson(String json) {
-    return new ApiResponse() {
-      @Override
-      public ResponseBody getResponseBody() {
-        return ResponseBody.create(JSON_MEDIA_TYPE, json);
-      }
-
-      @Override
-      public void close() {}
-    };
-  }
-
   private static final String MOCK_SESSION_STRING_1 =
       """
       {
@@ -338,7 +321,7 @@ public void listSessions_empty() {
   @Test
   public void listSessions_missingSessionsField_returnsEmpty() {
     when(mockApiClient.request("GET", "reasoningEngines/123/sessions?filter=user_id=userX", ""))
-        .thenReturn(apiResponseJson("{}"));
+        .thenAnswer(new MockApiAnswer("{}"));
 
     assertThat(vertexAiSessionService.listSessions("123", "userX").blockingGet().sessions())
         .isEmpty();
@@ -347,7 +330,7 @@ public void listSessions_missingSessionsField_returnsEmpty() {
   @Test
   public void listSessions_nullSessionsField_returnsEmpty() {
     when(mockApiClient.request("GET", "reasoningEngines/123/sessions?filter=user_id=userY", ""))
-        .thenReturn(apiResponseJson("{\"sessions\": null}"));
+        .thenAnswer(new MockApiAnswer("{\"sessions\": null}"));
 
     assertThat(vertexAiSessionService.listSessions("123", "userY").blockingGet().sessions())
         .isEmpty();