test_rng.py

"""Testing module for the RNG Model."""

import sys

import pecos as pc
from pecos.engines.cvm.rng_model import RNGModel


def test_set_seed() -> None:
    """Verifies that a seed is set properly for our RNG model."""
    rng = RNGModel(shot_id=0)
    seed = 42
    rng.set_seed(seed)
    assert rng.seed == seed


def test_random_number() -> None:
    """Verifies that the random number generated is an int type."""
    rng = RNGModel(shot_id=0)
    random = rng.rng_random()
    assert isinstance(random, int)


def test_bounded_random() -> None:
    """Verifies that a single generated random number is within bounds."""
    rng = RNGModel(shot_id=0)
    rng.set_seed(42)
    bound = 16
    rng.set_bound(bound)
    assert rng.current_bound == bound

    random_number = rng.rng_random()
    assert 0 <= random_number < bound


def test_set_idx_raises_for_backwards_index() -> None:
    """Verifies that an error is raised when specifying an index that was already consumed in the RNG stream."""
    rng = RNGModel(shot_id=0)
    rng.set_seed(42)

    rng.set_index(4)

    try:
        rng.set_index(3)
    except ValueError as exc:
        expected_error_msg = "RNGindex(3) cannot move backward: current stream index is 4"
        assert str(exc) == expected_error_msg


def test_set_idx() -> None:
    """Verifies that the idx is set properly for our model."""
    rng = RNGModel(shot_id=0)
    rng.set_seed(42)
    idx = 4
    rng.set_index(idx)
    assert rng.count == idx


def test_multiple_bounded_rand() -> None:
    """For several randomly generated number, with a random bound, verifies that its appropriate."""
    rng = RNGModel(shot_id=0)
    rng.set_seed(42)

    # Use platform-appropriate upper bound for randint
    # Windows: i32 max is 2^31 - 1 (2147483647), Unix: i64 allows 2^32
    max_bound = 2**31 - 1 if sys.platform == "win32" else 2**32

    for _ in range(100):
        random_bound = int(pc.random.randint(1, max_bound, 1)[0])
        rng.set_bound(random_bound)
        random_number = rng.rng_random()
        assert 0 <= random_number < random_bound