Simplify fill-tests.el by grouping similar tests in the same
erts file.  Move the test code into the erts files, so it is
closer to the test cases, which provides context.  Add basic
test cases for common filling operations and for the scenarios
described in Bug#79575.

* test/lisp/textmodes/fill-tests.el (fill-test-end-period)
(fill-test-haskell): Rename from `test-fill-end-period' and
`test-fill-haskell' to follow the same naming convention of
the other tests.
(fill-test-fill-region-as-paragraph-default)
(fill-test-fill-region-as-paragraph-semlf)
(fill-test-fill-region-as-paragraph, fill-test-fill-region)
(fill-test-fill-paragraph, fill-test-fill-paragraph-semlf):
Group tests and move test code into erts files.
(fill-test-fill-paragraph-semlf-emacs-lisp-mode)
(fill-test-fill-paragraph-semlf-c-mode)
(fill-test-fill-paragraph-semlf-org-mode)
(fill-test-fill-paragraph-semlf-markdown-mode): Rename from
`fill-test-semlf-emacs-lisp-mode', `fill-test-semlf-c-mode',
`fill-test-semlf-org-mode' and
`fill-test-semlf-markdown-mode'.  Move test code into erts
files.
(fill-test-semlf, fill-test-semlf-fill-region)
(fill-test-semlf-justify)
(fill-test-semlf-sentence-end-double-space)
(fill-test-semlf-fill-column)
(fill-test-semlf-punctuation-marks, fill-test-semlf-twice)
(fill-test-semlf-fill-prefix, fill-test-semlf-indented-block)
(fill-test-semlf-revert): Delete tests since they are now
grouped with other tests.

* test/lisp/textmodes/fill-resources/fill-paragraph.erts:
* test/lisp/textmodes/fill-resources/fill-paragraph-semlf.erts:
* test/lisp/textmodes/fill-resources/fill-region-as-paragraph.erts:
* test/lisp/textmodes/fill-resources/fill-region-as-paragraph-default.erts:
* test/lisp/textmodes/fill-resources/fill-region-as-paragraph-semlf.erts:
Add test cases for the function specified in the file name,
including tests for the scenarios described in the bug report.
* test/lisp/textmodes/fill-resources/fill-region.erts: Add
test case for custom `fill-region-as-paragraph-function',
include test code in the test specification.
* test/lisp/textmodes/fill-resources/fill-paragraph-semlf-c-mode.erts:
* test/lisp/textmodes/fill-resources/
fill-paragraph-semlf-emacs-lisp-mode.erts:
* test/lisp/textmodes/fill-resources/fill-paragraph-semlf-markdown-mode.erts:
* test/lisp/textmodes/fill-resources/fill-paragraph-semlf-org-mode.erts:
Rename from semlf-*-mode.erts, prefix test names with the
tested function and include test code in the test
specification.
* test/lisp/textmodes/fill-resources/semlf-fill-column.erts:
* test/lisp/textmodes/fill-resources/semlf-fill-prefix.erts:
* test/lisp/textmodes/fill-resources/semlf-fill-region.erts:
* test/lisp/textmodes/fill-resources/semlf-fill-region-as-paragraph.erts:
* test/lisp/textmodes/fill-resources/semlf-indented-block.erts:
* test/lisp/textmodes/fill-resources/semlf-justify.erts:
* test/lisp/textmodes/fill-resources/semlf-punctuation-marks.erts:
* test/lisp/textmodes/fill-resources/semlf-revert.erts:
* test/lisp/textmodes/fill-resources/semlf-sentence-end-double-space.erts:
* test/lisp/textmodes/fill-resources/semlf-twice.erts:
* test/lisp/textmodes/fill-resources/semlf.erts: Delete
files.  (Bug#79575)

* lisp/textmodes/ispell.el (ispell-add-per-file-word-list): Deal
with `comment-end' in a way that works for comments that don’t
nest.

We proceed as follows: when `comment-end' is non-empty, we only
ever insert one start and one end comment, the first time we add
a local word.  This works with both C-style (which don’t nest)
and Rust-style comments (which do).

If we’re using line comments (i.e. comments that only have a
`comment-start'), then continue to insert one on each line.

* test/lisp/textmodes/ispell-tests/ispell-tests.el
(ispell/ispell-add-per-file-word-list/nxml): Adjust test.

Bug#79871

* test/lisp/textmodes/ispell-resources/fake-aspell-new.bash
Error with a broken dictionary.

* test/lisp/textmodes/ispell-tests/ispell-tests-common.el
(ispell-tests--constants/nonexistent-dictionary): Add.
(ispell-tests--some-valid-dictionary): Give fallback dictionary.

* test/lisp/textmodes/ispell-tests/ispell-tests.el
(ispell/ispell-accept-buffer-local-defs/received-file): Use
proper broken dictionary.

Fixes bug#79477 and bug#79514

* test/lisp/textmodes/ispell-tests/ispell-hunspell-tests.el
(ispell-tests-hunspell--hunspell-working): Implement checker.
(ispell/hunspell/ispell-word/russian/check-only): Add skip-check.
(ispell/hunspell/ispell-word/english/check-only): Add skip-check.
(ispell/hunspell/ispell-word/language-switch/check-only): Add
skip-check.
(ispell/hunspell/ispell-word/russian/check-only/wrong-language): Add
skip-check.
(ispell/hunspell/ispell-word/multilang): Add skip-check.
* test/lisp/textmodes/ispell-tests/ispell-tests-common.el
(fake-aspell-path): Improve checking that an engine works.
(ispell-tests--letopt): Make restoring variables more robust,
rename to a local name.  Add debug spec.
(ispell-tests--with-ispell-global-dictionary): Rename to a local name
Add debug spec.
(ispell-tests--some-valid-dictionary): Add a selector for a safe
dictionary.
(ispell/ispell-accept-buffer-local-defs/received-file): Add.
(ispell-tests--constants/english/correct-list): Add.
(ispell-tests--constants/english/correct-one): Add.
(ispell-tests--constants/english/wrong): Add.
(ispell-tests--constants/russian/correct): Add.
(ispell-tests--constants/russian/wrong): Add.
(ispell-tests--constants/completion): Add.
* test/lisp/textmodes/ispell-tests/ispell-tests.el
(ispell/ispell-buffer-local-words/ispell-buffer-session-localwords):
reverse letopt and with-ispell-dictionary.
(ispell/ispell-buffer-local-words/ispell-words-keyword):
reverse letopt and with-ispell-dictionary.
(ispell/ispell-complete-word-interior-frag/simple):
reverse letopt and with-ispell-dictionary.
(ispell/ispell-complete-word/ispell-completion-at-point):
reverse letopt and with-ispell-dictionary.
(ispell/ispell-init-process/works-with-home):
reverse letopt and with-ispell-dictionary.
(ispell/ispell-kill-ispell):
reverse letopt and with-ispell-dictionary.
* test/lisp/textmodes/ispell-resources/fake-aspell-new.bash:
Add comments on unused function.  Replace echo with printf.

* test/lisp/textmodes/ispell-resources/fake-aspell-new.bash:
Avoid using associative arrays since they are not available
in old bash versions that come with some systems (bug#79177).

* test/lisp/textmodes/ispell-tests/ispell-aspell-tests.el:
* test/lisp/textmodes/ispell-tests/ispell-tests.el: Fix declare-function.

* test/lisp/textmodes/ispell-tests/ispell-aspell-tests.el:
* test/lisp/textmodes/ispell-tests/ispell-hunspell-tests.el:
* test/lisp/textmodes/ispell-tests/ispell-international-ispell-tests.el:
* test/lisp/textmodes/ispell-tests/ispell-tests.el: Fix load argument.

* lisp/textmodes/ispell.el (ispell-accept-output): Fix variable init.

* test/lisp/textmodes/ispell-resources/fake-aspell-new.bash:
Update mock aspell to be able to serve all tests.

* test/lisp/textmodes/ispell-tests/ispell-aspell-tests.el:
(ispell/aspell/ispell-word/english/correct): Implement.
(ispell/aspell/ispell-word/english/incorrect): Implement.
(ispell/aspell/ispell-word/english/wrong-language): Implement.

* test/lisp/textmodes/ispell-tests/ispell-hunspell-tests.el
Fix byte compilation errors.

* test/lisp/textmodes/ispell-international-ispell-tests.el
Fix byte compilation errors.

* test/lisp/textmodes/ispell-tests/ispell-tests-common.el
(with-ispell-global-dictionary): Implement a macro to
set and restore ispell.el's global dictionary.

* test/lisp/textmodes/ispell-tests/ispell-tests.el:
(ispell/ispell-buffer-local-words/ispell-words-keyword): Fix CI run.
(ispell/ispell-accept-buffer-local-defs/simple): Fix skip condition.
(ispell/ispell--run-on-word/default): Fix skip condition.
(ispell/ispell-word/default/check-only/correct): Fix global variable.
(ispell/ispell-word/default/check-only/correct/add-init): Fix
global variable.
(ispell/ispell-word/default/check-only/incorrect): Fix skip condition.
(ispell/ispell-region/incorrect): Fix postcondition.
(ispell/ispell-call-process/simple): Fix emacs path.
(ispell/ispell-call-process/simple-writable): Fix emacs path.
(ispell/ispell-call-process-region/cat-empty): Fix emacs path.
(ispell/ispell-call-process-region/cat-random): Fix emacs path.
(ispell/ispell-kill-ispell): Implement.
(ispell/ispell/buffer): Implement.
(ispell/ispell/region): Implement.
(ispell/ispell-change-dictionary): Implement.
(ispell/ispell-comments-and-strings/correct): Implement.
(ispell/ispell-comments-and-strings/incorrect): Implement.
(ispell/ispell-comment-or-string-at-point): Implement.
(ispell/ispell-pdict-save): Implement.
(ispell/ispell-pdict-save/force): Implement.
(ispell/ispell-pdict-save/modified): Implement.
(ispell/ispell-pdict-save/unmodified): Implement.
(ispell/ispell-lookup-words/simple): Implement.
(ispell/ispell-complete-word/ispell-completion-at-point): Implement.
(ispell/ispell-complete-word-interior-frag/simple): Implement.
(ispell/ispell-minor-mode/simple): Implement.
(ispell/ispell-message/correct): Implement.
(ispell/ispell-message/incorrect): Implement.