fix: include experiment key on local-eval exposure events

packages/node/src/exposure/exposure-service.ts

@@ -66,6 +66,10 @@ export const toExposureEvents = (
     } else if (variant.value) {
       eventProperties['[Experiment] Variant'] = variant.value;
     }
+    const experimentKey = variant.metadata?.experimentKey as string | undefined;
+    if (experimentKey) {
+      eventProperties['[Experiment] Experiment Key'] = experimentKey;
+    }
     if (variant.metadata) {
       eventProperties['metadata'] = variant.metadata;
     }

packages/node/test/local/exposure/exposure-service.test.ts

@@ -84,10 +84,21 @@ test('exposure to event as expected', async () => {
       value: 'on',
     },
     empty_variant: {},
+    with_experiment_key: {
+      key: 'treatment',
+      value: 'treatment',
+      metadata: {
+        segmentName: 'All Other Users',
+        flagType: 'experiment',
+        flagVersion: 10,
+        default: false,
+        experimentKey: 'exp-1',
+      },
+    },
   };
   const exposure = new Exposure(user, results);
   const events = toExposureEvents(exposure, DAY_MILLIS);
-  expect(events.length).toEqual(7); // Excludes default exposure.
+  expect(events.length).toEqual(8); // Excludes default exposure.
   for (const event of events) {
     expect(event.user_id).toEqual(user.user_id);
     expect(event.device_id).toEqual(user.device_id);
@@ -104,6 +115,12 @@ test('exposure to event as expected', async () => {
     );
     expect(eventProperties['metadata']).toEqual(results[flagKey].metadata);
 
+    if (flagKey === 'with_experiment_key') {
+      expect(eventProperties['[Experiment] Experiment Key']).toEqual('exp-1');
+    } else {
+      expect(eventProperties['[Experiment] Experiment Key']).toBeUndefined();
+    }
+
     // User Properties
     if (
       results[flagKey].metadata?.flagType === FLAG_TYPE_MUTUAL_EXCLUSION_GROUP
@@ -125,7 +142,7 @@ test('exposure to event as expected', async () => {
     }
 
     const canonicalization =
-      'user device basic control default off different_value on empty_metadata on holdout holdout mutex slot-1 partial_metadata on ';
+      'user device basic control default off different_value on empty_metadata on holdout holdout mutex slot-1 partial_metadata on with_experiment_key treatment ';
     const expected = `user device ${hashCode(
       flagKey + ' ' + canonicalization,
     )} ${Math.floor(exposure.timestamp / DAY_MILLIS)}`;