doc: Update PR checklist.

  Resolves numberscope#174.

doc/pull-request-checklist.md

@@ -5,13 +5,18 @@
 The PR submitter should:
 
 -   Please use a `snake_case` name for the branch in the PR.
--   Please limit your PR's focus to one thing.
+-   Please limit the PR's focus to one thing.
 -   Ideally, submit a small PR with limited functionality that can be built
     upon instead of submitting one huge, monolithic PR. Typically, the smaller
-    the PR, the better, with the obvious caveat that the code in your PR needs
+    the PR, the better, with the obvious caveat that the code in the PR needs
     to work and actually do something. A small PR for a visualizer might be in
     the ballpark of 200 lines of code.
--   Write or supplement test(s) for the file(s) you touch in your PR.
+-   Write or supplement test(s) for the file(s) affected by the PR. In
+    particular, if it is a bug fix PR, there **must** be a new test that would
+    fail with the prior code, but passes in the PR. The new tests may be
+    either unit (vitest) or end-to-end (Playwright) tests or both, as
+    appropriate.
+-   Update all documentation to reflect the changes in the PR.
 -   Make sure Numberscope runs properly, including former supposedly
     unmodified behaviors and newly implemented ones. In particular, run it via
     'npm run dev' and with the browser console open and make sure there are no
@@ -22,19 +27,24 @@ The PR submitter should:
 ## For PR reviewers
 
 -   All new or changed features are appropriately documented.
--   Tests are appropriately modified for all new or changed features.
+-   Tests are appropriately modified for all new or changed features. If it is
+    a bugfix PR there must be at least one new test. Most other PRs should
+    have new or changed tests as well. So if you do not see any changed files
+    in the e2e directory or in any **tests** directory, that is at least an
+    "orange" flag.
 -   The PR is passing lint by running `npm run lint`. There should be no
     changed files and no warnings/errors.
+-   The PR passes all tests. Note the GitHub CI infrastructure will check this
+    for you.
 -   The PR builds by running `npm run build`. (This also checks type
     correctness.) There should be no errors, and for now the only allowed
     warning is the one about some assets being too big.
--   The PR passes all tests. Right now (Oct. 2022), just by running
-    `npm run test:unit`.
--   Numberscope runs properly -- basically the same check as on the submitter
-    list, but be sure to exercise as many randomly selected behaviors as you
-    have time for, definitely including but not limited to the ones nominally
-    affected by the PR. This should be done in `npm run preview` mode after a
-    successful build.
+-   The built system runs with `npm run preview`.
+-   When run that way, Numberscope operates properly. The end-to-end tests
+    take the pressure to try a variety of random behaviors off of the
+    reviewer, but a number of possible actions that seem related to the
+    changes in the PR must definitely be tried in this fashion before
+    approving for merge.
 -   At the end of the review process, before merging, add a commit to update
     the
     ["Contributors" section of the "About" document](about.md#contributors) to