Here is a solution using Python under APIv1. Create the test and after 10 seconds retrieve the results. Assuming you pulled the active MX's serial or manually added it above this portion.
response = dashboard.devices.createDeviceLiveToolsThroughputTest(serial_number)
throughput_test_id = response['throughputTestId']
time.sleep(12)
response = dashboard.devices.getDeviceLiveToolsThroughputTest(serial_number, throughput_test_id)
print(f"Download throughput {response['result']['speeds']['downstream']}/Mbps")