Should fix:
```
rm -rf a b c
touch a
ln -s a b
mkdir c
./target/debug/coreutils cp --preserve=links -R -H a b c
a_inode=$(ls -i c/a|sed 's,c/.*,,')
b_inode=$(ls -i c/b|sed 's,c/.*,,')
echo "$a_inode" = "$b_inode"
```
prevents --preserve to eat the next argument when no value is passed.
default value for --preserve is set to mode,ownership(unix only),timestamps
before the patch:
cp --preserve foo bar
error: invalid value 'foo' for '--preserve [<ATTR_LIST>...]'
[possible values: mode, ownership, timestamps, context, link, links, xattr, all]
Signed-off-by: Guillaume Ranquet <granquet@baylibre.com>
Summary of changes in UCommand:
* Extend UCommand by builder methods and simplify methods in TestScenario
* Simplify code structures where possible. Add documentation.
* Store bin_path as PathBuf and util_name as String in all structs
* Remove UCommand::util and make bin_path, temp_dir private
* Rename UCommand::with_limit -> UCommand::limit
Summary of changes in TestScenario:
* Rename some parameters in TestScenario methods to be more descriptive
* Remove ucmd_keepenv, cmd_keepenv from TestScenario. Use UCommand::keep_env instead.
Summary of changes in tests/util:
* Introduce global constant TESTS_BINARY holding the path to `coreutils`
* Implement running an arbitrary command in a sh or cmd shell per default.
* Implement std::fmt::Display for UCommand.
* Change usages of UCommand::util_name from &Option<OsStr> to Option<OsStr>
* `UCommand::new_from_tmp`: Use OsStr directly instead of TempDir -> String -> OsStr
* Collect arguments in `UCommand::args` field
* Build environment variables in `UCommand` itself instead of `std::process::Command`
* Move building of std::process:Command from fields in UCommand to own method `build`
* Remove assertions of UCommand::has_run in arg, args and env.
Summary of changes in tests/by-util:
* Remove usages of UCommand::raw. Fix tests to use UCommand::to_string.
* test_test: Adjust test_invalid_utf8_integer_compare to use `UCommand::args`
* test_chmod: run_single_test
* test_pwd: symlinked_env
* test_cp:
Fix the usage of &Option<OsStr> in `test_src_base_dot`
Refactor test_src_base_dot to not use UCommand::new but ts.ucmd() instead
