Embodiments utilize a unified testing framework (UTF) to automate browser-based API testing of web applications. Embodiments cause a browser to generate an authentication context for a user of the web application, and then test API functionality based on the established authentication context. The UTF is configured to run both UI testing and API testing. Furthermore, in order to facilitate running multiple API tests in a given testing session (potentially being performed in parallel), the UTF stores results of a given API test in a corresponding data island DOM node. Each data island node, generated for each respective API test being run in a given testing session, is identified by a unique global unique identifier (GUID) that is associated with the corresponding API test. Using this GUID, the UTF accesses the test results of each API test individually as the test results are asynchronously returned by the remote service being tested.