effect-ts-laws/src/arbitrary/equivalence.js

effect-ts law testing using fast-check.

/**
 * Predicates for statistical testing of equality between functions.
 * @module
 */
import { Boolean as BO, Option as OP, pipe } from 'effect';
import { constFalse, constTrue } from 'effect/Function';
import fc from 'fast-check';
/**
 * Attempt to find an example input where the pair of given unary functions
 * is not equal. Given an arbitrary of `A`, an equivalence for `B` and a
 * pair of functions, check the functions compute the same `B` given the
 * same `A`, for `numRuns` values. Returns none or some value found.
 * @param a - An arbitrary for the function argument type `A`.
 * @param equalsB - Equivalence for the function return value type `B`.
 * @param parameters - Optional [fast-check parameters](https://fast-check.dev/api-reference/interfaces/Parameters.html).
 * @returns `none` if no counterexample to the equivalence was found, else
 * `some` of the `A` that was found to produce different values.
 * @category equivalence
 */
export const findCounterexample = (a, equalsB, parameters) => (
/**
 * First function to sample.
 */
self, 
/**
 * Second function to sample.
 */
that) => {
    const samples = fc.sample(a, parameters);
    /* v8 ignore next 1 */
    if (samples.length === 0)
        throw new Error('Empty sample.');
    for (const a of samples)
        if (!equalsB(self(a), that(a)))
            return OP.some(a);
    return OP.none();
};
/**
 * Attempt to find an example input where the pair of given unary functions
 * is not equal. Given an arbitrary of `A`, an equivalence for `B` and a
 * pair of functions, check the functions compute the same `B` given the
 * same `A`, for `numRuns` values. Returns a boolean flag indicating
 * equivalence.
 * @param a - An arbitrary for the function argument type `A`.
 * @param equalsB - Equivalence for the function return value type `B`.
 * @param parameters - Optional [fast-check parameters](https://fast-check.dev/api-reference/interfaces/Parameters.html).
 * @returns True if no counterexample found, else false.
 * @category equivalence
 */
export const testUnaryEquivalence = (a, equalsB, parameters) => (
/**
 * First function to sample.
 */
self, 
/**
 * Second function to sample.
 */
that) => pipe(findCounterexample(a, equalsB, parameters)(self, that), OP.match({
    onNone: constTrue,
    onSome: constFalse,
}));
/**
 * Same as `testUnaryEquivalence` but for functions of type `Endo<A>`.
 * @param a - An arbitrary for the function argument type `A`.
 * @param equalsA - Equivalence for the type `A`.
 * @param parameters - Optional [fast-check parameters](https://fast-check.dev/api-reference/interfaces/Parameters.html).
 * @returns True if no counterexample found, else false.
 * @category equivalence
 */
export const testEndoEquivalence = (a, equalsA, parameters) => (
/**
 * First function to sample.
 */
self, 
/**
 * Second function to sample.
 */
that) => testUnaryEquivalence(a, equalsA, parameters)(self, that);
/**
 * Same as `testUnaryEquivalence` but for functions of type `Predicate<A>`.
 * @param a - An arbitrary for the function argument type `A`.
 * @param parameters - Optional [fast-check parameters](https://fast-check.dev/api-reference/interfaces/Parameters.html).
 * @returns True if no counterexample found, else false.
 * @category equivalence
 */
export const testPredicateEquivalence = (a, parameters) => testUnaryEquivalence(a, BO.Equivalence, parameters);
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