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_exists.pl

@@ -0,0 +1,20 @@
+:- use_module(library(files)).
+:- use_module(library(os), [setenv/2, getenv/2]).
+
+check :-
+    act(TargetDir),
+    ground(TargetDir).
+
+act(TargetDir) :-
+    getenv("TARGET_DIRECTORY", TargetDir),
+	\+ directory_exists(TargetDir),
+	throw(existence_error(directory,TargetDir)).
+act(TargetDir) :-
+    getenv("TARGET_DIRECTORY", TargetDir),
+    directory_exists(TargetDir).
+
+main :-
+	setenv("TARGET_DIRECTORY", "."),
+	check.
+
+:- initialization(main).