lib.fileset: Fix shellcheck warnings in tests

\s*`root`: root "'"$work"'/foo/mock-root"

\s*`fileset`: root "'"$work"'/bar/mock-root"

\s*Different roots are not supported.'

rm -rf *

rm -rf -- *

# `root` needs to exist

expectFailure 'toSource { root = ./a; fileset = ./.; }' 'lib.fileset.toSource: `root` \('"$work"'/a\) does not exist.'

expectFailure 'toSource { root = ./a; fileset = ./a; }' 'lib.fileset.toSource: `root` \('"$work"'/a\) is a file, but it should be a directory instead. Potential solutions:

\s*- If you want to import the file into the store _without_ a containing directory, use string interpolation or `builtins.path` instead of this function.

\s*- If you want to import the file into the store _with_ a containing directory, set `root` to the containing directory, such as '"$work"', and set `fileset` to the file path.'

rm -rf *

rm -rf -- *

# The fileset argument should be evaluated, even if the directory is empty

expectFailure 'toSource { root = ./.; fileset = abort "This should be evaluated"; }' 'evaluation aborted with the following error message: '\''This should be evaluated'\'

expectFailure 'toSource { root = ./a; fileset = ./.; }' 'lib.fileset.toSource: `fileset` could contain files in '"$work"', which is not under the `root` \('"$work"'/a\). Potential solutions:

\s*- Set `root` to '"$work"' or any directory higher up. This changes the layout of the resulting store path.

\s*- Set `fileset` to a file set that cannot contain files outside the `root` \('"$work"'/a\). This could change the files included in the result.'

rm -rf *

rm -rf -- *

# Path coercion only works for paths

expectFailure 'toSource { root = ./.; fileset = 10; }' 'lib.fileset.toSource: `fileset` is of type int, but it should be a file set or a path instead.'

\s*element 0: root "'"$work"'/foo/mock-root"

\s*element 1: root "'"$work"'/bar/mock-root"

\s*Different roots are not supported.'

rm -rf *

rm -rf -- *

# Coercion errors show the correct context

expectFailure 'toSource { root = ./.; fileset = union ./a ./.; }' 'lib.fileset.union: first argument \('"$work"'/a\) does not exist.'