fix: previewVariants should fire impression events (#235)

Author: tyiuhc

packages/experiment-tag/src/experiment.ts

@@ -135,6 +135,9 @@ export class DefaultWebExperimentClient implements WebExperimentClient {
       Object.keys(variants).forEach((variantKey) => {
         this.flagVariantMap[key][variantKey] =
           convertEvaluationVariantToVariant(variants[variantKey]);
+        this.flagVariantMap[key][variantKey].metadata = {
+          deliveryMethod: 'web',
+        };
       });
 
       if (metadata.evaluationMode !== 'local') {

packages/experiment-tag/test/experiment.test.ts

@@ -330,7 +330,14 @@ describe('initializeExperiment', () => {
       'http://test.com/',
     );
     expect(mockExposureInternal).toHaveBeenCalledWith('test', {
-      variant: { key: 'control', value: 'control' },
+      variant: {
+        key: 'control',
+        value: 'control',
+        metadata: {
+          deliveryMethod: 'web',
+          url: 'http://localhost/',
+        },
+      },
       source: 'local-evaluation',
       hasDefaultVariant: false,
     });