feat(js): Add current repetition property to jestlike test wrapper (#1856)

### Problem
When running tests with multiple repetitions using LangSmith's
Jest/Vitest test wrapper, there's no way to get the current repetition
number.

### Solution
This PR adds an `repetition` property that gets passed to the test
function, providing the current repetition index

### Use Case
For multi-turn conversations, each repetition needs its own unique
threadId that remains consistent throughout all tests in that
conversation.

```javascripts
const ConversationTestDataset = [{
    inputs: {
      userId: "test-user-123",
      message: "What's the weather like today?",
      conversationId: "weather-chat",
    },
    referenceOutputs: {
      responseType: "weather_info",
      requiresLocation: true,
    },
  },
  {
    inputs: {
      userId: "test-user-123", 
      message: "How about tomorrow?",
      conversationId: "weather-chat",
    },
    referenceOutputs: {
      responseType: "forecast",
    },
  },
];

ls.describe("Conversation Flow Tests", () => {
  ls.test.each(ConversationTestDataset, {
    repetitions: 5,  // Run each test case 5 times
  })(
    "Multi-turn conversation",
    async ({ inputs, referenceOutputs, repetition }) => {
      // Now we can create unique thread IDs for each repetition
      const threadId = `${inputs.conversationId}-run-${repetition}`;
      
      const response = await conversationAgent({
        ...inputs,
        threadId,
      });

      // Validate response matches expected outputs
      expect(response.type).toBe(referenceOutputs.responseType);
      
      // Log outputs with repetition context
      ls.logOutputs({ 
        response: response.content,
        threadId,
        repetitionIndex: repetition 
      });
    }
  );
});
```

---------

Co-authored-by: jacoblee93 <[email protected]>

Author: tendev-liam

js/src/utils/jestlike/index.ts

@@ -34,6 +34,7 @@ import type {
   LangSmithJestlikeWrapperParams,
   LangSmithJestlikeDescribeWrapper,
   LangSmithJestlikeDescribeWrapperConfig,
+  LangSmithJestlikeTestFunction,
 } from "./types.js";
 import { getEnvironmentVariable, isJsDom } from "../env.js";
 import {
@@ -465,9 +466,7 @@ export function generateWrapperFromJestlikeMethods(
     >(
       name: string,
       lsParams: LangSmithJestlikeWrapperParams<I, O>,
-      testFn: (
-        data: { inputs: I; referenceOutputs?: O } & Record<string, any>
-      ) => unknown | Promise<unknown>,
+      testFn: LangSmithJestlikeTestFunction<I, O>,
       timeout?: number
     ) {
       // Due to https://github.com/jestjs/jest/issues/13653,
@@ -572,6 +571,13 @@ export function generateWrapperFromJestlikeMethods(
                           ...rest,
                           inputs: testInput,
                           referenceOutputs: testOutput,
+                          testMetadata: {
+                            exampleId,
+                            experimentId: project?.id,
+                            datasetId: dataset?.id,
+                            testTrackingEnabled: trackingEnabled(testContext),
+                            repetition: i,
+                          },
                         }
                       )
                     );
@@ -767,12 +773,7 @@ export function generateWrapperFromJestlikeMethods(
       }
       return function (
         name: string,
-        fn: (
-          params: { id?: string; inputs: I; referenceOutputs?: O } & Record<
-            string,
-            any
-          >
-        ) => unknown | Promise<unknown>,
+        fn: LangSmithJestlikeTestFunction<I, O>,
         timeout?: number
       ) {
         for (let i = 0; i < table.length; i += 1) {

js/src/utils/jestlike/types.ts

@@ -42,3 +42,20 @@ export type SimpleEvaluationResult = {
   score: NonNullable<EvaluationResult["score"]>;
   comment?: EvaluationResult["comment"];
 };
+
+export type LangSmithJestlikeTestMetadata = {
+  exampleId?: string;
+  experimentId?: string;
+  datasetId?: string;
+  testTrackingEnabled: boolean;
+  repetition: number;
+};
+
+export type LangSmithJestlikeTestFunction<I, O> = (
+  data: {
+    inputs: I;
+    referenceOutputs?: O;
+    testMetadata: LangSmithJestlikeTestMetadata;
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  } & Record<string, any>
+) => unknown | Promise<unknown>;