Interface: Parameters<T>

Defined in: packages/fast-check/src/check/runner/configuration/Parameters.ts:11

Customization of the parameters used to run the properties

Remarks

Since 0.0.6

Type Parameters

Type Parameter	Default type
T	void

Properties

asyncReporter?

optional asyncReporter?: (runDetails) => Promise<void>

Defined in: packages/fast-check/src/check/runner/configuration/Parameters.ts:193

Replace the default reporter handling errors by a custom one

Reporter is responsible to throw in case of failure: default one throws whenever runDetails.failed is true. But you may want to change this behaviour in yours.

Only used when calling assert Cannot be defined in conjonction with reporter Not compatible with synchronous properties: runner will throw

Parameters

Parameter	Type
runDetails	RunDetails<T>

Returns

Promise<void>

Remarks

Since 1.25.0

---

endOnFailure?

optional endOnFailure?: boolean

Defined in: packages/fast-check/src/check/runner/configuration/Parameters.ts:168

Stop run on failure

It makes the run stop at the first encountered failure without shrinking.

When used in complement to seed and path, it replays only the minimal counterexample.

Remarks

Since 1.11.0

---

examples?

optional examples?: T[]

Defined in: packages/fast-check/src/check/runner/configuration/Parameters.ts:157

Custom values added at the beginning of generated ones

It enables users to come with examples they want to test at every run

Remarks

Since 1.4.0

---

ignoreEqualValues?

optional ignoreEqualValues?: boolean

Defined in: packages/fast-check/src/check/runner/configuration/Parameters.ts:122

Discard runs corresponding to already tried values.

WARNING: Discarded runs will not be replaced. In other words, if you ask for 100 runs and have 2 discarded runs you will only have 98 effective runs.

NOTE: Relies on fc.stringify to check the equality.

Remarks

Since 2.14.0

---

includeErrorInReport?

optional includeErrorInReport?: boolean

Defined in: packages/fast-check/src/check/runner/configuration/Parameters.ts:205

By default the Error causing the failure of the predicate will not be directly exposed within the message of the Error thown by fast-check. It will be exposed by a cause field attached to the Error.

The Error with cause has been supported by Node since 16.14.0 and is properly supported in many test runners.

But if the original Error fails to appear within your test runner, Or if you prefer the Error to be included directly as part of the message of the resulted Error, you can toggle this flag and the Error produced by fast-check in case of failure will expose the source Error as part of the message and not as a cause.

---

interruptAfterTimeLimit?

optional interruptAfterTimeLimit?: number

Defined in: packages/fast-check/src/check/runner/configuration/Parameters.ts:91

Interrupt test execution after a given time limit: disabled by default

NOTE: Relies on Date.now().

NOTE: Useful to avoid having too long running processes in your CI. Replay capability (see seed, path) can still be used if needed.

WARNING: If the test got interrupted before any failure occured and before it reached the requested number of runs specified by numRuns it will be marked as success. Except if markInterruptAsFailure has been set to true

Remarks

Since 1.19.0

---

markInterruptAsFailure?

optional markInterruptAsFailure?: boolean

Defined in: packages/fast-check/src/check/runner/configuration/Parameters.ts:97

Mark interrupted runs as failed runs if preceded by one success or more: disabled by default Interrupted with no success at all always defaults to failure whatever the value of this flag.

Remarks

Since 1.19.0

---

maxSkipsPerRun?

optional maxSkipsPerRun?: number

Defined in: packages/fast-check/src/check/runner/configuration/Parameters.ts:51

Maximal number of skipped values per run

Skipped is considered globally, so this value is used to compute maxSkips = maxSkipsPerRun * numRuns. Runner will consider a run to have failed if it skipped maxSkips+1 times before having generated numRuns valid entries.

See pre for more details on pre-conditions

Remarks

Since 1.3.0

---

numRuns?

optional numRuns?: number

Defined in: packages/fast-check/src/check/runner/configuration/Parameters.ts:40

Number of runs before success: 100 by default

Remarks

Since 1.0.0

---

path?

optional path?: string

Defined in: packages/fast-check/src/check/runner/configuration/Parameters.ts:128

Way to replay a failing property directly with the counterexample. It can be fed with the counterexamplePath returned by the failing test (requires seed too).

Remarks

Since 1.0.0

---

randomType?

optional randomType?: RandomType | ((seed) => any)

Defined in: packages/fast-check/src/check/runner/configuration/Parameters.ts:35

Random number generator: xorshift128plus by default

Random generator is the core element behind the generation of random values - changing it might directly impact the quality and performances of the generation of random values. It can be one of: 'mersenne', 'congruential', 'congruential32', 'xorshift128plus', 'xoroshiro128plus' Or any function able to build a RandomGenerator based on a seed

As required since pure-rand v6.0.0, when passing a builder for RandomGenerator, the random number generator must generate values between -0x80000000 and 0x7fffffff.

Remarks

Since 1.6.0

---

reporter?

optional reporter?: (runDetails) => void

Defined in: packages/fast-check/src/check/runner/configuration/Parameters.ts:180

Replace the default reporter handling errors by a custom one

Reporter is responsible to throw in case of failure: default one throws whenever runDetails.failed is true. But you may want to change this behaviour in yours.

Only used when calling assert Cannot be defined in conjonction with asyncReporter

Parameters

Parameter	Type
runDetails	RunDetails<T>

Returns

void

Remarks

Since 1.25.0

---

seed?

optional seed?: number

Defined in: packages/fast-check/src/check/runner/configuration/Parameters.ts:22

Initial seed of the generator: Date.now() by default

It can be forced to replay a failed run.

In theory, seeds are supposed to be 32-bit integers. In case of double value, the seed will be rescaled into a valid 32-bit integer (eg.: values between 0 and 1 will be evenly spread into the range of possible seeds).

Remarks

Since 0.0.6

---

skipAllAfterTimeLimit?

optional skipAllAfterTimeLimit?: number

Defined in: packages/fast-check/src/check/runner/configuration/Parameters.ts:74

Skip all runs after a given time limit: disabled by default

NOTE: Relies on Date.now().

NOTE: Useful to stop too long shrinking processes. Replay capability (see seed, path) can resume the shrinking.

WARNING: It skips runs. Thus test might be marked as failed. Indeed, it might not reached the requested number of successful runs.

Remarks

Since 1.15.0

---

skipEqualValues?

optional skipEqualValues?: boolean

Defined in: packages/fast-check/src/check/runner/configuration/Parameters.ts:110

Skip runs corresponding to already tried values.

WARNING: Discarded runs will be retried. Under the hood they are simple calls to fc.pre. In other words, if you ask for 100 runs but your generator can only generate 10 values then the property will fail as 100 runs will never be reached. Contrary to ignoreEqualValues you always have the number of runs you requested.

NOTE: Relies on fc.stringify to check the equality.

Remarks

Since 2.14.0

---

timeout?

optional timeout?: number

Defined in: packages/fast-check/src/check/runner/configuration/Parameters.ts:58

Maximum time in milliseconds for the predicate to answer: disabled by default

WARNING: Only works for async code (see asyncProperty), will not interrupt a synchronous code.

Remarks

Since 0.0.11

---

unbiased?

optional unbiased?: boolean

Defined in: packages/fast-check/src/check/runner/configuration/Parameters.ts:138

Force the use of unbiased arbitraries: biased by default

Remarks

Since 1.1.0

---

verbose?

optional verbose?: boolean | VerbosityLevel

Defined in: packages/fast-check/src/check/runner/configuration/Parameters.ts:149

Enable verbose mode: VerbosityLevel.None by default

Using verbose: true is equivalent to verbose: VerbosityLevel.Verbose

It can prove very useful to troubleshoot issues. See VerbosityLevel for more details on each level.

Remarks

Since 1.1.0

Methods

logger()?

optional logger(v): void

Defined in: packages/fast-check/src/check/runner/configuration/Parameters.ts:133

Logger (see statistics): console.log by default

Parameters

Parameter	Type
v	string

Returns

void

Remarks

Since 0.0.6