`default_missing_value` set to `OPT_DATE` (`"date"`)
`num_args(0..=1)` required for `default_missing_value`.
Using function name `test_date_rfc_8601_default`.
The function name `test_date_rfc_8601` is left intact for
compatibility.
Fixes: #4521
* tests/util: Fix documentation of UCommand::stderr_only and usage_error
* tests/util: Remove trimming from CmdResult::stdout_matches and stdout_does_not_match. Fix tests.
The tests are fixed to match the trailing newline instead of ignoring it.
`LANGUAGE=C` is not enough, `LC_ALL=C` is needed as the environment
variable that overrides all the other localization settings.
e.g.
```bash
$ LANGUAGE=C id foobar
id: ‘foobar’: no such user
$ LC_ALL=C id foobar
id: 'foobar': no such user
```
* replace `LANGUAGE` with `LC_ALL` as environment variable in the tests
* fix the the date string of affected uutils
* replace `‘` and `’` with `'`
refactor `is_wsl` to `is_wsl_1` and `is_wsl_2`
On my tests with wsl2 ubuntu2004 all tests pass without special cases
I moved wsl detection into uucore so that it can be shared instead of duplicated
I moved `parse_mode` into uucode as it seemed to fit there better and anyway requires libc feature
* date: change tests to expect failure
Although these tests contain valid dates, the parsing logic is not
implemented yet. It should be changed to expect success when
the parsing logic is done.
* date: fix test build errors
* date: implement set date for unix and windows
Parsing the date string is not fully implemented yet, as in it relies
on the internals of chrono - things like "Mon, 14 Aug 2006 02:34:56 -0600"
do not work, nor does "2006-08-14 02:34:56" (no TZ / local time). This
is no different to using the "--date" option however, and will get fixed
when `parse_date` is a bit smarter.
Only supports unix and Windows platforms for now.
