Bootstrap mechanism

[simonharris]

With a view to:

• test file autodiscovery: save user having to explicitly specify every test file for PlUnit to look at
• streamline test output. swipl + plunit can be a little verbose, and this might be a good location to rein it in a little
• gymnastics to allow capturing source variable names (see Capture actual variable names in feedback (advanced) #33)
• ...

[simonharris]

1. You run your runner (not swipl -g ... run_tests)
2. Your runner scans for test files (test_*.pl, *_test.pl, whatever convention)
3. For each test file, instead of consult/1, you do read_term/3 with variable_names/1
   • Store the mapping somewhere (like a dict keyed by test clause)
   • Then actually assert/compile the clause into the database so PlUnit sees it normally
4. When assert_equals/2 fires and fails, you can look up that test’s mapping and pretty-print with real names

:- module(test_loader, [load_tests/1, run_all_tests/0]).

:- dynamic var_mapping/3.
% var_mapping(File, ClauseHead, Names).
% Names is a list like [A='A',B='B',Code='Code'].

load_tests(File) :-
    setup_call_cleanup(
        open(File, read, In),
        load_terms(In, File),
        close(In)
    ).

load_terms(In, File) :-
    read_term(In, Term, [variable_names(Names)]),
    (   Term == end_of_file
    ->  true
    ;   record_term(File, Term, Names),
        assertz(Term),             % "play it forward" so PlUnit sees test/1 etc.
        load_terms(In, File)
    ).

record_term(File, Term, Names) :-
    (   Term = (:- _)
    ->  true                       % skip directives
    ;   functor(Term, Head, Arity),
        var_mapping(File, Head/Arity, _)
    ->  true                       % already recorded
    ;   assertz(var_mapping(File, Term, Names))
    ).

Later, in your assert_equals/2 failure path, you’d call something like:

pretty_vars(Term, Pretty) :-
    var_mapping(_File, _Clause, Names),
    copy_term(Term, TermCopy),
    numbervars(TermCopy, 0, _),
    maplist(bind_pretty, Names),
    with_output_to(string(Pretty), portray_clause(TermCopy)).

...and instead of _2894+_2896#<_2890, you’d get something closer to B+C #< D.

[simonharris]

We could probably just expose a predicate run_tests/N that users can run via swipl -g or from within the repl. Arguments might specify the file search path (backwards compatibility with existing PlUnit tests).