Prolog Testing

---
name: prolog-testing
description: Standardized instructions and frameworks for writing and running Prolog unit tests across engines (Scryer testing.pl, SWI plunit, Trealla/ISO).
---

# Prolog Testing Standards

Use this skill when writing, running, or configuring unit tests for Prolog code.

## Scryer Prolog (Primary / Default Engine)

For Scryer Prolog, use [`testing.pl`](https://github.com/bakaq/testing.pl).

### Installing / Referencing `testing.pl`
Fetch `testing.pl` into the project's test directory or library path:
```prolog
:- use_module(library(testing)).
```
Or reference a local `testing.pl` module:
```prolog
:- use_module('tests/testing.pl').
```

### Writing Tests in Scryer Prolog
Use `test/1` or `test/2` predicates:
```prolog
:- use_module(library(testing)).

test(pure_addition) :-
    X = 3,
    Y = 4,
    Z is X + Y,
    Z == 7.

test(dcg_parse) :-
    phrase("hello", `hello`).
```

### Running Scryer Prolog Tests Safely
Always run tests using `scryer-safe`:
```bash
scryer-safe -g run_tests -t halt tests/test_suite.pl
```

---

## SWI-Prolog Testing

For SWI-Prolog, use `library(plunit)`.

```prolog
:- use_module(library(plunit)).

:- begin_tests(basic_tests).

test(addition) :-
    X is 2 + 2,
    X == 4.

:- end_tests(basic_tests).
```

### Running SWI-Prolog Tests Safely
```bash
swi-safe -g "run_tests,halt" tests/test_suite.pl
```

---

## Trealla & Tau Prolog / Portable ISO Testing

For Trealla, Tau Prolog CLI, or generic ISO engines, write pure assertion runner predicates evaluated via `trealla-safe`, `tau-safe`, or `prolog-safe`.

```prolog
run_all_tests :-
    (   test_clause1, test_clause2 ->
        write('ALL TESTS PASSED'), nl, halt(0)
    ;   write('TEST FAILURE'), nl, halt(1)
    ).
```

### Running CLI Tests Safely:
```bash
# Trealla Prolog
trealla-safe -g "run_all_tests,halt" tests/test_suite.pl

# Tau Prolog CLI
tau-safe -g "run_all_tests,halt" tests/test_suite.pl
```

---

## Tau Prolog JavaScript / Node.js Embedded Testing

For Tau Prolog embedded in JavaScript applications or Node.js test runners (Jest, Mocha, Vitest, Node test runner):

```javascript
const pl = require("tau-prolog");

describe("Tau Prolog Test Suite", () => {
    let session;

    beforeEach(() => {
        session = pl.create(1000);
    });

    test("addition query", (done) => {
        session.query("X is 2 + 2.", {
            success: () => {
                session.answer((answer) => {
                    expect(session.format_answer(answer)).toBe("X = 4.");
                    done();
                });
            }
        });
    });
});
```