fix: 🐛 ensure setRequestHeader monkey patch matches real world usage

Author: gingerbenw

packages/request-tracker/lib/xhr-tracker.js

@@ -35,7 +35,7 @@ function createXhrTracker (global, options = {}) {
         const requestData = trackedRequests.get(this)
         if (requestData) {
           requestData.headers = requestData.headers || {}
-          requestData.headers[String(header)] = String(value)
+          requestData.headers[String(header)] = (requestData.headers[String(header)] || '') + String(value)
         }
       }
       originalSetRequestHeader.apply(this, arguments)

test/browser/features/fixtures/http_errors/src/app.tsx

@@ -9,6 +9,8 @@ function xhrGet () {
   const xhr = new XMLHttpRequest()
   xhr.open('GET', `${REFLECT_ENDPOINT}?status=404&userId=12345`)
   xhr.setRequestHeader('X-Token', 'super-secret-token')
+  xhr.setRequestHeader('X-Test-Value', 'one-two')
+  xhr.setRequestHeader('X-Test-Value', '-three-four')
   xhr.send()
 }
 

test/browser/features/http_errors.feature

@@ -86,6 +86,7 @@ Feature: HTTP Errors
     And the error payload field "events.0.request.url" equals the stored value "expected.request.url"
     And the event "request.httpMethod" equals "GET"
     And the event "request.headers.X-Token" equals "[REDACTED]"
+    And the event "request.headers.X-Test-Value" equals "one-two-three-four"
     And the event "request.params.status" equals "404"
     And the event "request.params.userId" equals "[REDACTED]"
     And the event "request.body" is null