This is a testharness.js-based test.
[FAIL] the result of compressing [,Hello,Hello] with brotli should be 'HelloHello'
  promise_test: Unhandled rejection with value: object "TypeError: Failed to construct 'CompressionStream': Unsupported compression format: 'brotli'"
[FAIL] the result of compressing [Hello,,Hello] with brotli should be 'HelloHello'
  promise_test: Unhandled rejection with value: object "TypeError: Failed to construct 'CompressionStream': Unsupported compression format: 'brotli'"
[FAIL] the result of compressing [Hello,Hello,] with brotli should be 'HelloHello'
  promise_test: Unhandled rejection with value: object "TypeError: Failed to construct 'CompressionStream': Unsupported compression format: 'brotli'"
Harness: the test ran to completion.