diff --git a/lib/multipart.js b/lib/multipart.js
index f4d429b1aa..90682aedda 100644
--- a/lib/multipart.js
+++ b/lib/multipart.js
@@ -28,8 +28,10 @@ const multipartDataGenerator = (method, data, headers) => {
     return `"${s.replace(/"|"/g, '%22').replace(/\r\n|\r|\n/g, ' ')}"`;
   }
 
-  for (const k in utils.flattenAndStringify(data)) {
-    const v = data[k];
+  const flattenedData = utils.flattenAndStringify(data);
+
+  for (const k in flattenedData) {
+    const v = flattenedData[k];
     push(`--${segno}`);
     if (v.hasOwnProperty('data')) {
       push(
diff --git a/testUtils/index.js b/testUtils/index.js
index fdca468709..78a8693821 100644
--- a/testUtils/index.js
+++ b/testUtils/index.js
@@ -56,8 +56,22 @@ const utils = (module.exports = {
         if (host) {
           req.host = host;
         }
-        stripeInstance.REQUESTS.push(req);
-        cb.call(this, null, {});
+
+        const handleMockRequest = (err, req) => {
+          stripeInstance.REQUESTS.push(req);
+          cb.call(this, err, {});
+        };
+
+        if (this.requestDataProcessor) {
+          this.requestDataProcessor(
+            method,
+            data,
+            options.headers,
+            handleMockRequest
+          );
+        } else {
+          handleMockRequest(null, req);
+        }
       };
     }