add tests for file module predicates

reproduce failing `directory_exists/1` with working directory passed as first argument
reproduce failing `delete_directory/1` with ./test directory passed as first argument
reproduce failing `file_size/1` with 2 bytes files passed as first argument
reproduce failing `file_exists/1` with existing file passed as first argument
reproduce failing `file_modification_time/1`, `file_access_time/1` and `file_creation_time/1` with existing file passed as first argument
reproduce failing `directory_files/2` with existing directory passed as first argument
reproduce failing `delete_file/1` with existing file passed as first argument
reproduce failing `make_directory/1` with non-existing directory passed as first argument
reproduce failing `make_directory_path/1` with non-existing path passed as first argument
reproduce failing `path_canonical/2` with non-canonical path passed as first argument
reproduce failing `rename_file/2` with existing file passed as first argument, target file as second arg
revised `directory_exists/1` test case
renamed test files, test directories
use `path_segments/2`, remove path separators
do not write file size to current output
revised `directory_files/2` test
revised `path_canonical/2` test
revised `file_exists/1` test
removed hardcoded expected size
extracted hardcoded directory argument
remove path prefix containing path separator
revised expected ls cmd exit code so that it is platform-agnostic

Signed-off-by: Thierry Marianne <thierry@marianne.io>

tests-pl/issue_directory_files.pl

@@ -0,0 +1,30 @@
+:- use_module(library(files)).
+:- use_module(library(iso_ext)).
+:- use_module(library(lists)).
+:- use_module(library(os), [setenv/2, getenv/2, shell/2]).
+
+check :-
+    act(TargetDirectory, Files),
+    ground(TargetDirectory),
+    length(Files, N),
+    write(N).
+
+act(TargetDirectory, Files) :-
+    getenv("TARGET_DIRECTORY", TargetDirectory),
+    directory_files(TargetDirectory, Files).
+
+main :-
+    path_segments(Path, ["directory_files_test_parent", "directory_files_test_file"]),
+    call_cleanup(
+       (setenv("TARGET_DIRECTORY", "directory_files_test_parent"),
+        shell("test -d directory_files_test_parent || mkdir directory_files_test_parent", 0),
+        append(["test -e ", Path, " || touch ", Path], Cmd),
+        shell(Cmd, 0),
+        check),
+       (append(["rm -f ", Path, " || true"], Cmd1),
+        shell(Cmd1, 0),
+        shell("rmdir directory_files_test_parent || true", 0),
+        shell("ls directory_files_test_parent", 1))
+    ).
+
+:- initialization(main).