Testing

Clausal has two kinds of tests: Python-level pytest tests in tests/, and inline Test/1 clauses in .clausal files.

Inline Test/1 clauses

Any .clausal file (see Syntax) can include test clauses of the form:

Test("description") <- goal1, goal2, ...

A test passes if its body succeeds (produces at least one solution). Tests live alongside the predicates they exercise:

Fib(0, 0),
Fib(1, 1),
Fib(N, F) <- (
    N > 1,
    N1 == N - 1,
    N2 == N - 2,
    Fib(N1, F1),
    Fib(N2, F2),
    F == F1 + F2
)

Test("fib(5) = 5") <- Fib(5, 5)
Test("fib(7) = 13") <- (Fib(7, F), F == 13)

Running .clausal tests standalone

Use clausal.testing as a command-line tool:

# Run all .clausal files under a directory
python -m clausal.testing clausal/examples/

# Run a single file
python -m clausal.testing clausal/examples/fibonacci.clausal

# Verbose output (shows individual PASS/FAIL)
python -m clausal.testing -v clausal/examples/

The exit code is 0 if all tests pass, 1 otherwise.

Running .clausal tests via pytest

The conftest.py at the project root registers a pytest plugin that automatically collects .clausal files. The import hook handles loading and compilation. Each Test/1 clause appears as an individual pytest item:

python -m pytest clausal/examples/fibonacci.clausal -v

Output looks like:

clausal/examples/fibonacci.clausal::fib(0) = 0 PASSED
clausal/examples/fibonacci.clausal::fib(5) = 5 PASSED

This means .clausal tests and Python tests can run together in one pytest invocation. Imported Prolog .pl files with Test/1 clauses can also be tested — see Importing Prolog.

Running Python tests

python -m pytest tests/ -q

Note: tests/test_continuation_search.py requires greenlet and is skipped if not installed.

Writing good Test/1 clauses

• Each test should be a single rule with a descriptive string as the argument.
• Test bodies can use any predicates defined in the module, plus builtins like append, Member, etc.
• Use == for CLP(ℤ) arithmetic equality on computed results: Test("check") <- (SomePred(X), X == expected). For ground integers this behaves like equality; for Vars it posts a CLP(ℤ) constraint.
• Use structural_eq(X, Y) for structural equality (Prolog ==/2) when comparing non-integer terms.
• Use == for arithmetic: Test("arith") <- (N == 2 + 3, N == 5).

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See also: Examples — for real test predicates used in example programs.