howitworks-assert-end.js

miniFc.property = (generator, predicate) => {
    return {
        generate(mrng) {
            return generator.generate(mrng);
        },
        shrink(value) {
            return generator.shrink(value);
        },
        run(valueUnderTest) {
            return predicate(valueUnderTest);
        }
    }
}

function executeAndShrink(valueUnderTest, property) {
    if (!property.run(valueUnderTest)) {
        for (const shrunkValue of property.shrink(valueUnderTest)) {
            const shrunkResults = executeAndShrink(shrunkValue, property);
            if (shrunkResults.failed) {
                return shrunkResults;
            }
        }
        return { failed: true, value: valueUnderTest };
    }
    return { failed: false };
}

miniFc.assert = (property, { seed = Date.now() } = {}) => {
    let rng = prand.xoroshiro128plus(seed);
    for (let runId = 0 ; runId !== 100 ; ++runId) {
        const valueUnderTest = property.generate(new Random(rng));
        const testResults = executeAndShrink(valueUnderTest, property);
        if (testResults.failed) {
            throw new Error(`Property failed after ${runId + 1} runs with value ${JSON.stringify(testResults.value)} (seed: ${seed})`);
        }
        rng = rng.jump();
    }
}