update example

examples/node-package/index.js

@@ -3,7 +3,15 @@ import promptfoo from '../../dist/src/index.js';
 (async () => {
   const results = await promptfoo.evaluate({
     prompts: ['Rephrase this in French: {{body}}', 'Rephrase this like a pirate: {{body}}'],
-    providers: ['openai:gpt-3.5-turbo'],
+    providers: [
+      'openai:gpt-3.5-turbo',
+      (prompt) => {
+        // Call LLM here...
+        return {
+          output: '<LLM output>',
+        };
+      },
+    ],
     tests: [
       {
         vars: {
@@ -14,6 +22,19 @@ import promptfoo from '../../dist/src/index.js';
         vars: {
           body: "I'm hungry",
         },
+        assert: [
+          {
+            type: 'javascript',
+            value: (output) => {
+              const pass = output.includes("J'ai faim");
+              return {
+                pass,
+                score: pass ? 1.0 : 0.0,
+                reason: pass ? 'Output contained substring' : 'Output did not contain substring',
+              };
+            },
+          },
+        ],
       },
     ],
   });