This is a testharness.js-based test.
[FAIL] ":heading" should be a valid selector
  Failed to execute 'querySelector' on 'Document': ':heading' is not a valid selector.
[FAIL] ":heading(2)" should be a valid selector
  Failed to execute 'querySelector' on 'Document': ':heading(2)' is not a valid selector.
[FAIL] ":heading(99999)" should be a valid selector
  Failed to execute 'querySelector' on 'Document': ':heading(99999)' is not a valid selector.
[FAIL] ":heading(0)" should be a valid selector
  Failed to execute 'querySelector' on 'Document': ':heading(0)' is not a valid selector.
[FAIL] ":heading(0, 1, 2)" should be a valid selector
  Failed to execute 'querySelector' on 'Document': ':heading(0, 1, 2)' is not a valid selector.
[FAIL] ":heading(0, 1, 2, 3, 4, 5, 6, 7, 8, 9)" should be a valid selector
  Failed to execute 'querySelector' on 'Document': ':heading(0, 1, 2, 3, 4, 5, 6, 7, 8, 9)' is not a valid selector.
[FAIL] ":heading(-1)" should be a valid selector
  Failed to execute 'querySelector' on 'Document': ':heading(-1)' is not a valid selector.
[FAIL] "h1:heading" should be a valid selector
  Failed to execute 'querySelector' on 'Document': 'h1:heading' is not a valid selector.
[FAIL] "h1:heading(1)" should be a valid selector
  Failed to execute 'querySelector' on 'Document': 'h1:heading(1)' is not a valid selector.
[FAIL] "h1:heading(2)" should be a valid selector
  Failed to execute 'querySelector' on 'Document': 'h1:heading(2)' is not a valid selector.
Harness: the test ran to completion.