This is a testharness.js-based test.
[FAIL] response.headers.get('content-length') expects 0
  promise_test: Unhandled rejection with value: object "TypeError: Failed to fetch"
[FAIL] response.headers.get('content-length') expects 0, 0
  promise_test: Unhandled rejection with value: object "TypeError: Failed to fetch"
[FAIL] response.headers.get('double-trouble') expects , 
  promise_test: Unhandled rejection with value: object "TypeError: Failed to fetch"
[FAIL] response.headers.get('foo-test') expects 1, 2, 3
  promise_test: Unhandled rejection with value: object "TypeError: Failed to fetch"
[FAIL] response.headers.get('heya') expects , , 1, , , 2
  promise_test: Unhandled rejection with value: object "TypeError: Failed to fetch"
[FAIL] response.headers.get('www-authenticate') expects 1, 2, 3, 4
  promise_test: Unhandled rejection with value: object "TypeError: Failed to fetch"
Harness: the test ran to completion.