fix: update reflection API E2E Test (#3529)

Author: huangjeff5

tests/specs/reflection_api.yaml

@@ -34,3 +34,12 @@ tests:
           role: model
           content:
             - text: '{"messages":[{"content":[{"text":"hello"}],"role":"user"}]}'
+        usage:
+          inputCharacters: 5
+          outputCharacters: 59
+          inputImages: 0
+          inputVideos: 0
+          inputAudioFiles: 0
+          outputImages: 0
+          outputVideos: 0
+          outputAudioFiles: 0

tests/test_js_app/src/index.ts

@@ -14,7 +14,8 @@
  * limitations under the License.
  */
 
-import { genkit, z } from 'genkit';
+import { MessageData, genkit, z } from 'genkit';
+import { getBasicUsageStats } from 'genkit/model';
 
 const ai = genkit({
   plugins: [],
@@ -30,16 +31,18 @@ ai.defineModel(
     // So swap the order here to match Go.
     const m = input.messages[0];
     input.messages[0] = { content: m.content, role: m.role };
+    const message: MessageData = {
+      role: 'model',
+      content: [
+        {
+          text: JSON.stringify(input),
+        },
+      ],
+    };
     return {
       finishReason: 'stop',
-      message: {
-        role: 'model',
-        content: [
-          {
-            text: JSON.stringify(input),
-          },
-        ],
-      },
+      message,
+      usage: getBasicUsageStats(input.messages, message),
     };
   }
 );