Class Arbitrary<T>Abstract

Check if a given value could be pass to shrink without providing any context.

In general, canShrinkWithoutContext is not designed to be called for each shrink but rather on very special cases. Its usage must be restricted to canShrinkWithoutContext or in the rare* contexts of a shrink method being called without any context. In this ill-formed case of shrink, canShrinkWithoutContext could be used or called if needed.

*we fall in that case when fast-check is asked to shrink a value that has been provided manually by the user, in other words: a value not coming from a call to generate or a normal shrink with context.

Remarks

Since 3.0.0

Create another arbitrary by mapping a value from a base Arbirary using the provided fmapper Values produced by the new arbitrary are the result of the arbitrary generated by applying fmapper to a value

Example

const arrayAndLimitArbitrary = fc.nat().chain((c: number) => fc.tuple( fc.array(fc.nat(c)), fc.constant(c)));
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Remarks

Since 1.2.0

Create another arbitrary by filtering values against predicate

All the values produced by the resulting arbitrary satisfy predicate(value) == true

Be aware that using filter may highly impact the time required to generate a valid entry

Example

const integerGenerator: Arbitrary<number> = ...;
const evenIntegerGenerator: Arbitrary<number> = integerGenerator.filter(e => e % 2 === 0);
// new Arbitrary only keeps even values
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Remarks

Since 1.23.0

Create another arbitrary by filtering values against predicate

All the values produced by the resulting arbitrary satisfy predicate(value) == true

Be aware that using filter may highly impact the time required to generate a valid entry

Example

const integerGenerator: Arbitrary<number> = ...;
const evenIntegerGenerator: Arbitrary<number> = integerGenerator.filter(e => e % 2 === 0);
// new Arbitrary only keeps even values
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Remarks

Since 0.0.1

Generate a value of type T along with its context (if any) based on the provided random number generator

Remarks

Since 0.0.1 (return type changed in 3.0.0)

Create another arbitrary by mapping all produced values using the provided mapper Values produced by the new arbitrary are the result of applying mapper value by value

Example

const rgbChannels: Arbitrary<{r:number,g:number,b:number}> = ...;
const color: Arbitrary<string> = rgbChannels.map(ch => `#${(ch.r*65536 + ch.g*256 + ch.b).toString(16).padStart(6, '0')}`);
// transform an Arbitrary producing {r,g,b} integers into an Arbitrary of '#rrggbb'
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Remarks

Since 0.0.1

Create another Arbitrary that cannot be biased

Remarks

Since 1.1.0

Create another Arbitrary with no shrink values

Example

const dataGenerator: Arbitrary<string> = ...;
const unshrinkableDataGenerator: Arbitrary<string> = dataGenerator.noShrink();
// same values no shrink
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Remarks

Since 0.0.9

Shrink a value of type T, may rely on the context previously provided to shrink efficiently

Must never be called with possibly invalid values and no context without ensuring that such call is legal by calling canShrinkWithoutContext first on the value.

Remarks

Since 3.0.0