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* Predicates for statistical testing of equality between functions.
* @module
*/
import {Boolean as BO, Equivalence as EQ, 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, B>(
a: fc.Arbitrary<A>,
equalsB: EQ.Equivalence<B>,
parameters?: fc.Parameters<A>,
) =>
(
/**
* First function to sample.
*/
self: (a: A) => B,
/**
* Second function to sample.
*/
that: typeof self,
): OP.Option<A> => {
const samples: A[] = 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, B>(
a: fc.Arbitrary<A>,
equalsB: EQ.Equivalence<B>,
parameters?: fc.Parameters<A>,
) =>
(
/**
* First function to sample.
*/
self: (a: A) => B,
/**
* Second function to sample.
*/
that: typeof self,
): boolean =>
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>(
a: fc.Arbitrary<A>,
equalsA: EQ.Equivalence<A>,
parameters?: fc.Parameters<A>,
) =>
(
/**
* First function to sample.
*/
self: (a: A) => A,
/**
* Second function to sample.
*/
that: typeof self,
): boolean =>
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>(
a: fc.Arbitrary<A>,
parameters?: fc.Parameters<A>,
) => testUnaryEquivalence(a, BO.Equivalence, parameters)
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