Documentation: .serviceworker implies .https these days (#18295)

See discussion at web-platform-tests/wpt#18228.

Author: annevk

docs/writing-tests/file-names.md

@@ -58,6 +58,8 @@ themselves precede any test type flag, but are otherwise unordered.
    context why the test is tentative and what needs to be resolved to make it
    non-tentative.
 
+It's preferable that `.window`, `.worker`, and `.any` are immediately followed
+by their final `.js` extension.
 
 [server-side substitution]: https://wptserve.readthedocs.io/en/latest/pipes.html#sub
 [RFC 2119]: https://tools.ietf.org/html/rfc2119

docs/writing-tests/general-guidelines.md

@@ -32,7 +32,8 @@ css/ directory, regardless of where they are in the directory structure.
 
 By default, tests are served over plain HTTP. If a test requires HTTPS
 it must be given a filename containing `.https` before the extension,
-e.g. `test-secure.https.html`. For more details see the documentation
+e.g., `test-secure.https.html`, or be the generated service worker test
+of a `.https`-less `.any` test. For more details see the documentation
 on [file names][file-name-flags].
 
 #### Support Files

docs/writing-tests/testharness.md

@@ -165,7 +165,7 @@ are:
 
 * `window` (default): to be run at <code><var>x</var>.any.html</code>
 * `dedicatedworker` (default): to be run at <code><var>x</var>.any.worker.html</code>
-* `serviceworker`: to be run at <code><var>x</var>.https.any.serviceworker.html</code>
+* `serviceworker`: to be run at <code><var>x</var>.any.serviceworker.html</code> (`.https` is implied)
 * `sharedworker`: to be run at <code><var>x</var>.any.sharedworker.html</code>
 * `jsshell`: to be run in a JavaScript shell, without access to the DOM
   (currently only supported in SpiderMonkey, and skipped in wptrunner)