### Setup Project with Bun

Source: https://fast-check.dev/docs/tutorials/quick-start/basic-setup

Use Bun to download the project template and install dependencies.

```bash
bun x degit dubzzz/fast-check/website/templates/fast-check-tutorial fast-check-tutorial  

cd fast-check-tutorial  

npm i  

```

--------------------------------

### Setup Project with pnpm

Source: https://fast-check.dev/docs/tutorials/quick-start/basic-setup

Use pnpm to download the project template and install dependencies.

```bash
pnpm dlx degit dubzzz/fast-check/website/templates/fast-check-tutorial fast-check-tutorial  

cd fast-check-tutorial  

npm i  

```

--------------------------------

### Setup Project with npm

Source: https://fast-check.dev/docs/tutorials/quick-start/basic-setup

Use npm to download the project template and install dependencies.

```bash
npx degit dubzzz/fast-check/website/templates/fast-check-tutorial fast-check-tutorial  

cd fast-check-tutorial  

npm i  

```

--------------------------------

### Setup Project with Yarn

Source: https://fast-check.dev/docs/tutorials/quick-start/basic-setup

Use Yarn to download the project template and install dependencies.

```bash
yarn dlx degit dubzzz/fast-check/website/templates/fast-check-tutorial fast-check-tutorial  

cd fast-check-tutorial  

npm i  

```

--------------------------------

### Install fast-check and @fast-check/jest with Bun

Source: https://fast-check.dev/docs/tutorials/setting-up-your-test-environment/property-based-testing-with-jest

Install the necessary libraries for your project using Bun.

```bash
bun add --dev fast-check @fast-check/jest  
```

--------------------------------

### Install @fast-check/vitest with Bun

Source: https://fast-check.dev/docs/tutorials/setting-up-your-test-environment/property-based-testing-with-vitest

Install the necessary libraries for property-based testing with Vitest using Bun.

```bash
bun add --dev fast-check @fast-check/vitest  

```

--------------------------------

### Install fast-check with Bun

Source: https://fast-check.dev/docs/introduction/getting-started

Install fast-check as a development dependency using Bun.

```bash
bun add --dev fast-check
```

--------------------------------

### Install fast-check and @fast-check/jest with npm

Source: https://fast-check.dev/docs/tutorials/setting-up-your-test-environment/property-based-testing-with-jest

Install the necessary libraries for your project using npm.

```bash
npm install --save-dev fast-check @fast-check/jest  
```

--------------------------------

### Install @fast-check/vitest with npm

Source: https://fast-check.dev/docs/tutorials/setting-up-your-test-environment/property-based-testing-with-vitest

Install the necessary libraries for property-based testing with Vitest using npm.

```bash
npm install --save-dev fast-check @fast-check/vitest  

```

--------------------------------

### Install experimental fast-check with Bun

Source: https://fast-check.dev/docs/introduction/getting-started

Install the latest experimental version of fast-check from pkg.pr.new using Bun. Use with caution as APIs may be unstable.

```bash
bun add --dev https://pkg.pr.new/fast-check@main
```

--------------------------------

### Install fast-check with pnpm

Source: https://fast-check.dev/docs/introduction/getting-started

Install fast-check as a development dependency using pnpm.

```bash
pnpm add --save-dev fast-check
```

--------------------------------

### Vitest Setup File for Global Settings

Source: https://fast-check.dev/docs/configuration/global-settings

Import `fast-check` and call `configureGlobal` within the Vitest setup file.

```javascript
import fc from 'fast-check';
fc.configureGlobal({ numRuns: 10 });
```

--------------------------------

### Install fast-check and @fast-check/jest with pnpm

Source: https://fast-check.dev/docs/tutorials/setting-up-your-test-environment/property-based-testing-with-jest

Install the necessary libraries for your project using pnpm.

```bash
pnpm add --save-dev fast-check @fast-check/jest  
```

--------------------------------

### Install @fast-check/vitest with pnpm

Source: https://fast-check.dev/docs/tutorials/setting-up-your-test-environment/property-based-testing-with-vitest

Install the necessary libraries for property-based testing with Vitest using pnpm.

```bash
pnpm add --save-dev fast-check @fast-check/vitest  

```

--------------------------------

### Install fast-check with Yarn

Source: https://fast-check.dev/docs/introduction/getting-started

Install fast-check as a development dependency using Yarn.

```bash
yarn add --dev fast-check
```

--------------------------------

### Install fast-check and @fast-check/jest with Yarn

Source: https://fast-check.dev/docs/tutorials/setting-up-your-test-environment/property-based-testing-with-jest

Install the necessary libraries for your project using Yarn.

```bash
yarn add --dev fast-check @fast-check/jest  
```

--------------------------------

### Install @fast-check/vitest with Yarn

Source: https://fast-check.dev/docs/tutorials/setting-up-your-test-environment/property-based-testing-with-vitest

Install the necessary libraries for property-based testing with Vitest using Yarn.

```bash
yarn add --dev fast-check @fast-check/vitest  

```

--------------------------------

### Install experimental fast-check with Yarn

Source: https://fast-check.dev/docs/introduction/getting-started

Install the latest experimental version of fast-check from pkg.pr.new using Yarn. Use with caution as APIs may be unstable.

```bash
yarn add --dev https://pkg.pr.new/fast-check@main
```

--------------------------------

### Install fast-check with npm

Source: https://fast-check.dev/docs/introduction/getting-started

Install fast-check as a development dependency using npm.

```bash
npm install --save-dev fast-check
```

--------------------------------

### Per-Test Settings Example

Source: https://fast-check.dev/docs/configuration/global-settings

Demonstrates how to specify settings like `numRuns` for individual tests.

```javascript
test('test #1', () => {
  fc.assert(myProp1, { numRuns: 10 });
});

test('test #2', () => {
  fc.assert(myProp2, { numRuns: 10 });
});

test('test #3', () => {
  fc.assert(myProp3, { numRuns: 10 });
});
```

--------------------------------

### Install experimental fast-check with npm

Source: https://fast-check.dev/docs/introduction/getting-started

Install the latest experimental version of fast-check from pkg.pr.new using npm. Use with caution as APIs may be unstable.

```bash
npm install --save-dev https://pkg.pr.new/fast-check@main
```

--------------------------------

### Install experimental fast-check with pnpm

Source: https://fast-check.dev/docs/introduction/getting-started

Install the latest experimental version of fast-check from pkg.pr.new using pnpm. Use with caution as APIs may be unstable.

```bash
pnpm add --save-dev https://pkg.pr.new/fast-check@main
```

--------------------------------

### Replay and Shrink Reported Errors

Source: https://fast-check.dev/docs/advanced/fuzzing

Replay a specific failing example and attempt to shrink it by setting `numRuns` to 1 and providing the example in the `examples` option.

```javascript
test('replay reported error and shrink it', () => {
  fc.assert(fc.property(...arbitraries, predicate), {
    numRuns: 1,
    examples: [
      [
        /* reported error */
      ],
    ],
  });
});
```

--------------------------------

### Jest Setup File for Global Settings

Source: https://fast-check.dev/docs/configuration/global-settings

Import `fast-check` and call `configureGlobal` within the Jest setup file.

```javascript
const fc = require('fast-check');
fc.configureGlobal({ numRuns: 10 });
```

--------------------------------

### Using Context with Custom Examples

Source: https://fast-check.dev/docs/configuration/user-definable-values

When using `context` for logging within a predicate, ensure your custom examples include a properly generated context instance.

```javascript
const exampleContext = () => fc.sample(fc.context(), { numRuns: 1 })[0];

fc.assert(fc.property(fc.string(), fc.string(), fc.context(), myCheckFunction), {
  examples: [['', '', exampleContext()]],
});
```

--------------------------------

### Define Custom Examples for One Parameter Property

Source: https://fast-check.dev/docs/configuration/user-definable-values

Provide a list of specific values to test against a property with a single parameter. These examples run before generated values and reduce the number of generated values tested.

```javascript
fc.assert(fc.property(fc.nat(), myCheckFunction), {
  examples: [
    [0],
    [Number.MAX_SAFE_INTEGER],
  ],
});
```

--------------------------------

### Example usage of statistics

Source: https://fast-check.dev/docs/core-blocks/runners

This example shows how to use the `statistics` runner with `fc.string()`. It classifies strings by their length and runs the analysis with 100,000 iterations.

```javascript
fc.statistics(
  fc.string(), // source arbitrary
  (v) => `${v.length} characters`, // classifier
  { numRuns: 100_000 }, // extra parameters
);
// Possible output:
// >  0 characters...9.65%
// >  2 characters...9.56%
// >  1 characters...9.41%
// >  3 characters...9.30%
// >  6 characters...9.04%
// >  9 characters...8.92%
// >  7 characters...8.90%
// >  8 characters...8.90%
// >  10 characters..8.86%
// >  4 characters...8.79%
// >  5 characters...8.68%
```

--------------------------------

### CommonJS Module Import Example

Source: https://fast-check.dev/blog/2023/09/04/dual-packages-or-supporting-both-cjs-and-esm

Demonstrates how to import modules in a CommonJS (CJS) environment, typically used in Node.js.

```javascript
const dep1 = require('dep1');  
const dep2 = require('dep2');  

```

--------------------------------

### Synchronous Property Example with fc.pre

Source: https://fast-check.dev/docs/core-blocks/properties

This example uses `fc.pre` to filter out invalid inputs (where label length exceeds maxLength) and returns a boolean to indicate success or failure.

```javascript
fc.property(fc.nat(), fc.string(), (maxLength, label) => {
  fc.pre(label.length <= maxLength); // any label such label.length > maxLength, will be dropped
  return crop(label, maxLength) === label; // true is success, false is failure
});
```

--------------------------------

### Vitest Configuration for Global Settings

Source: https://fast-check.dev/docs/configuration/global-settings

Configure Vitest to load global settings by specifying a setup file in `vitest.config.js`.

```javascript
import { defineConfig } from 'vitest/config';

export default defineConfig({
  test: {
    // ...
    setupFiles: ['./vitest.setup.js'],
  },
});
```

--------------------------------

### Synchronous Property with Setup/Teardown

Source: https://fast-check.dev/docs/core-blocks/properties

Leverage `.beforeEach` and `.afterEach` to add synchronous setup and teardown logic to your properties. These hooks can call previous hooks if they exist.

```javascript
fc.property(...arbitraries, (...args) => {})
  .beforeEach((previousBeforeEach) => {})
  .afterEach((previousAfterEach) => {});
```

--------------------------------

### Generated Object Examples

Source: https://fast-check.dev/docs/core-blocks/arbitraries/composites/object

Examples of objects generated by the configured object arbitrary, showcasing the diversity of data types and structures that can be produced.

```javascript
{}
```

```javascript
{"𐝥򾫽򄓎𥸕򽊶󱂝綖":{"򉘤𿴀􀡹񻞏􃆢󂼾󺉁𤻎󁑹󩨭":"new Number(5.458711183935786e+215)","\"\"":
```

```javascript
new Set([new Number(-168580940874959),false,new String("𱚏󗿥")])
```

```javascript
"𿚔\u0003":new Map([["󵒊󩇣󄠾󹓅",new String("􃷂󅧰􊧮򆬽尢纍񬏖򈢯")],[ "򂆶𮕉ɠ񩗢󜧡𞯧󥰆󪲳󲴥󏜠",new Number(-3.915309186966617e-201)],["񢬬󬘃񍦎𨴓򌥱򑲮󷋴󧡥󦹎񮮻",false],[ "󢎆򐵂􍨌𣏓⢋򄓢𰌂􃙼",9.778144932315068e-292],[ "󥓽򠕉",new Boolean(true)],["񳟟",new Number(7263738133547713)],["􈦶񈫡򒧯񮹡󬲒򈓠","񒂜򡌍􎅹󇤮󪶟򠿺󓸸񒴕"],["񤮇",""] ,["򰨞𧘻򪣵򄠏",new String("򿺔󴼃򷣧󓀒")]])
```

```javascript
"򇔎󻢢򶞇񙿢񏡂󕌴񠪢𤾿򇣦􉫽":Uint8ClampedArray.from([2,167,221,250,25,5,253,3,39])
```

```javascript
"񫍋󕪿󿫽񈬌񁷚":new Set([null,-7554992422397568,-17220778063163852213518299424149709632540904753173033601881880719429971665504n,new String(""),new Boolean(true),undefined,-10556040980590440407765974154662897970048173654375365677184296697937171159766n])
```

```javascript
"toString":{}
```

```javascript
"񂱹":[]
```

```javascript
"𺴕󖼑򠊅𔡹򁵩":Uint8ClampedArray.from([118,211,17])
```

```javascript
"n":"new Map([[\"",-3.847406447449319e-89]])"
```

```javascript
"\u0007\u0013򆡭\u0003諸\u0010\f":{__proto__:null,"񕯄􏿻\u000e\u0000\u000b𪲿󓕲\u0014":new Number(-7.4e-323),"󟔭򑂬𖄋񉾻𭩼𗿎򹸶臦":"", "":23060781171921571898756243128383982884697443490579335692025690551060929342872n,"u򰉠oStr":new String("򻝢󔔲𐬸򁭘񩃟򵶳񍏫𓹹򓠹򴻯"),"􏿼񺆁":null,"󅆲򚏵󪹫񌋬𮏄𚨛󉬐":new Number(-1.3004479422180178e+247)}}
```

--------------------------------

### Example of a timeout failure report

Source: https://fast-check.dev/docs/configuration/timeouts

This is an example of how a timeout failure report might appear. It indicates the property failed, provides details about the seed and path, shows the counterexample, and specifies the timeout limit that was exceeded.

```text
Uncaught Error: Property failed after 1 tests  
{ seed: 1234070620, path: "0:0", endOnFailure: true }  
Counterexample: [new Map([["my-package",{}]]),0]  
Shrunk 1 time(s)  
Got Property timeout: exceeded limit of 1000 milliseconds  
  
Hint: Enable verbose mode in order to have the list of all failing values encountered during the run  
    at buildError (/workspaces/fast-check/packages/fast-check/lib/check/runner/utils/RunDetailsFormatter.js:131:15)  
    at asyncThrowIfFailed (/workspaces/fast-check/packages/fast-check/lib/check/runner/utils/RunDetailsFormatter.js:148:11)  
    at runNextTicks (node:internal/process/task_queues:60:5)  
    at process.processTimers (node:internal/timers:509:9)  

```

--------------------------------

### Install fast-check JavaScript Testing Expert Skill

Source: https://fast-check.dev/docs/ai-powered-testing

Install the fast-check skill to your AI assistant using npx. This enables the AI to apply best practices for writing high-quality JavaScript tests.

```bash
npx skills add dubzzz/fast-check --skill javascript-testing-expert  
```

--------------------------------

### AMD Module Definition Example

Source: https://fast-check.dev/blog/2023/09/04/dual-packages-or-supporting-both-cjs-and-esm

Illustrates the syntax for defining modules using Asynchronous Module Definition (AMD), commonly used in browsers before ESM.

```javascript
requirejs(['dep1', 'dep2'], function (dep1, dep2) {
  
  // This function is called when dep1.js and dep2.js  

  // and their dependencies are loaded.  
});  

```

--------------------------------

### Configure Global Settings for fast-check

Source: https://fast-check.dev/docs/tutorials/setting-up-your-test-environment/property-based-testing-manual-setup

Use fc.configureGlobal to set shared configurations for all property-based tests. This example sets an interrupt time limit of 5000 milliseconds.

```javascript
const fc = require('fast-check');

fc.configureGlobal({ interruptAfterTimeLimit: 5_000 });
```

--------------------------------

### Example of skipAllAfterTimeLimit usage

Source: https://fast-check.dev/docs/configuration/timeouts

Illustrates the output when `skipAllAfterTimeLimit` causes a failure because no predicate succeeded before the timeout. This output shows the error message, run details, and hints for debugging.

```text
Failed to run property, too many pre-condition failures encountered  

{ seed: 1119647454 }  
  
Ran 0 time(s)  
Skipped 10001 time(s)  
  
Hint (1): Try to reduce the number of rejected values by combining map, chain and built-in arbitraries  
Hint (2): Increase failure tolerance by setting maxSkipsPerRun to an higher value  
Hint (3): Enable verbose mode at level VeryVerbose in order to check all generated values and their associated status  
    at buildError (/workspaces/fast-check/packages/fast-check/lib/check/runner/utils/RunDetailsFormatter.js:131:15)  
    at asyncThrowIfFailed (/workspaces/fast-check/packages/fast-check/lib/check/runner/utils/RunDetailsFormatter.js:148:11)  
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)  
```

--------------------------------

### yaml: Parsing Strings Starting with ':,'

Source: https://fast-check.dev/docs/introduction/track-record

This example shows that the `yaml` library fails to parse string values that start with ':,'. The `stringify` function produces valid YAML, but `parse` throws a `YAMLSyntaxError`.

```javascript
YAML.stringify([[':,']]); //=> '- - :,\n'  
YAML.parse('- - :,\n'); //=> YAMLSyntaxError: Document is not valid YAML (bad indentation?)  
```

--------------------------------

### Replace stringOf with string

Source: https://fast-check.dev/docs/migration-guide/from-3.x-to-4.x

Starting from v3.22.0, `stringOf` is recommended to be replaced by `string`. The example shows how to adapt the usage by passing the unit configuration to `fc.string`.

```typescript
-fc.stringOf(fc.constantFrom('Hello', 'World'));  
+fc.string({ unit: fc.constantFrom('Hello', 'World') });
```

--------------------------------

### Constructor

Source: https://fast-check.dev/docs/api/classes/Arbitrary

Initializes a new instance of the Arbitrary class.

```APIDOC
## Constructor

### Description
Initializes a new instance of the Arbitrary class.

### Signature
```typescript
new Arbitrary<T>(): Arbitrary<T>
```

### Returns
An instance of Arbitrary<T>.
```

--------------------------------

### IProperty Methods

Source: https://fast-check.dev/docs/api/interfaces/IProperty

This section details the methods available on the IProperty interface, including generate, isAsync, run, and shrink.

```APIDOC
## generate()

### Description
Generate values of type Ts.

### Parameters
- **mrng** (Random) - Random number generator.
- **runId?** (number) - Id of the generation, starting at 0 - if set the generation might be biased.

### Returns
Value<Ts>

## isAsync()

### Description
Is the property asynchronous? true in case of asynchronous property, false otherwise.

### Returns
false

## run()

### Description
Check the predicate for v.

### Parameters
- **v** (Ts) - Value of which we want to check the predicate.

### Returns
PreconditionFailure | PropertyFailure | null

## shrink()

### Description
Shrink value of type Ts.

### Parameters
- **value** (Value<Ts>) - The value to be shrunk, it can be context-less.

### Returns
Stream<Value<Ts>>
```

--------------------------------

### ModelRunAsyncSetup<Model, Real>

Source: https://fast-check.dev/docs/api/type-aliases/ModelRunAsyncSetup

An asynchronous setup function that generates both the model and real representations of a value. This is useful for scenarios where you need to perform checks on both the abstract model and the concrete real value.

```APIDOC
## Type Alias: ModelRunAsyncSetup<Model, Real>

> **ModelRunAsyncSetup** <`Model`, `Real`> = () => `Promise`<{ `model`: `Model`; `real`: `Real`; }>

Defined in: packages/fast-check/src/check/model/ModelRunner.ts:19

Asynchronous definition of model and real.

### Type Parameters

| Type Parameter | Description |
| -------------- | ----------- |
| `Model`        |             |
| `Real`         |             |

### Returns

- `Promise`<{ `model`: `Model`; `real`: `Real`; }>: A promise that resolves to an object containing the generated model and real values.
```

--------------------------------

### Re-run Configuration Options

Source: https://fast-check.dev/docs/tutorials/quick-start/read-test-reports

Details on how to use `path` and `endOnFailure` options when re-running tests. `path` starts execution on a reduced counterexample, and `endOnFailure` stops immediately on failure.

```text
{ seed: -1819918769, path: "0:...:3", endOnFailure: true }  
```

--------------------------------

### Shrink Custom Values for a Property

Source: https://fast-check.dev/docs/configuration/user-definable-values

Fast-check automatically shrinks user-defined examples if they fail, aiding in debugging. This example demonstrates shrinking a property that checks for the presence of a value in an array.

```javascript
function buildQuickLookup(values) {
  const fastValues = Object.fromEntries(values.map((value) => [value, true]));
  return { has: (value) => value in fastValues };
}

fc.assert(
  fc.property(fc.array(fc.string()), fc.string(), (allValues, lookForValue) => {
    const expectedResult = allValues.includes(lookForValue);
    const cache = buildQuickLookup(allValues);
    return cache.has(lookForValue) === expectedResult;
  }),
  {
    examples: [
      [[], '__proto__'],
    ],
  },
);
```

--------------------------------

### EntityGraphRelations Example

Source: https://fast-check.dev/docs/api/type-aliases/EntityGraphRelations

This example demonstrates the structure of EntityGraphRelations, defining relationships for 'employee' and 'team' entities. The 'employee' entity has 'manager' and 'team' relationships, while 'team' has no outgoing relationships defined.

```typescript
{
  
  employee: {
    
    manager: { arity: '0-1', type: 'employee' },
    
    team: { arity: '1', type: 'team' }
    
  },
  
  team: {}
  
}
```

--------------------------------

### run()

Source: https://fast-check.dev/docs/api/interfaces/Command

Executes the command on the system under test. It receives the non-updated model and the real system, performs post-execution checks, and throws an error if the state is invalid. It also updates the model accordingly.

```APIDOC
## run()

### Description
Receive the non-updated model and the real or system under test. Perform the checks post-execution - Throw in case of invalid state. Update the model accordingly.

### Parameters
#### Path Parameters
- **m** (Model) - Required - Model, simplified or schematic representation of real system
- **r** (Real) - Required - Sytem under test

### Returns
`void`

### Remarks
Since 1.5.0

### Inherited from
`ICommand`.`run`
```

--------------------------------

### Constructor

Source: https://fast-check.dev/docs/api/classes/Value

Initializes a new instance of the Value class.

```APIDOC
## new Value<T>(value_, context, customGetValue?)

### Description
Initializes a new instance of the Value class.

### Parameters
#### Parameters
- **value_** (T) - Internal value of the shrinkable
- **context** (unknown) - Context associated to the generated value (useful for shrink)
- **customGetValue?** (() => T) - Limited to internal usages (to ease migration to next), it will be removed on next major

### Returns
Value<T>
```

--------------------------------

### Run Tests with Bun

Source: https://fast-check.dev/docs/tutorials/quick-start/basic-setup

Execute the project's tests using the Bun run test command.

```bash
bun run test  

```

--------------------------------

### Run Bun Tests

Source: https://fast-check.dev/docs/tutorials/setting-up-your-test-environment/property-based-testing-with-bun-test-runner

Execute all tests defined in your project using the 'bun test' command in the terminal.

```bash
bun test
```

--------------------------------

### Updated entries with 'start' field for dichotomic search

Source: https://fast-check.dev/blog/2024/11/05/whats-new-in-fast-check-3-23-0

Shows the internal structure of entries with the added 'start' field, enabling dichotomic search for improved performance in 'mapToConstant'. This change allows for logarithmic complexity in locating the correct 'build' function.

```javascript
const entries = [
  { start: 0, num: 26, build: (v) => String.fromCharCode(v + 0x61) },
  { start: 26, num: 10, build: (v) => String.fromCharCode(v + 0x30) },
];
```

--------------------------------

### ModelRunSetup<Model, Real>

Source: https://fast-check.dev/docs/api/type-aliases/ModelRunSetup

Defines a synchronous function that returns an object containing 'model' and 'real' properties. This is used for setting up model-based property testing.

```APIDOC
## Type Alias: ModelRunSetup<Model, Real>

> **ModelRunSetup** <`Model`, `Real`> = () => `object`

Defined in: packages/fast-check/src/check/model/ModelRunner.ts:12

Synchronous definition of model and real.

### Type Parameters​

Type Parameter  
---
`Model`
`Real`

### Returns​

`object`

#### model​

> **model** : `Model`

#### real​

> **real** : `Real`

### Remarks​

Since 2.2.0
```

--------------------------------

### Filter Arbitrary for Odd Integers

Source: https://fast-check.dev/docs/core-blocks/arbitraries/combiners/any

This example demonstrates filtering for odd integers, showing the flexibility of the .filter combinator.

```javascript
fc.integer().filter((n) => n % 2 !== 0);
```

--------------------------------

### sample()

Source: https://fast-check.dev/docs/api/functions/sample

Generates an array containing all the values that would have been generated during assert or check.

```APIDOC
## Function: sample()
> **sample** <`Ts`>(`generator`, `params?`): `Ts`[]
Defined in: packages/fast-check/src/check/runner/Sampler.ts:62
Generate an array containing all the values that would have been generated during assert or check
## Type Parameters​
Type Parameter  
---
`Ts`
## Parameters​
Parameter| Type| Description  
---|---|---
`generator`| `IRawProperty`<`Ts`, `boolean`> | `Arbitrary`<`Ts`>| IProperty or Arbitrary to extract the values from  
`params?`| `number` | `Parameters`<`Ts`>| Integer representing the number of values to generate or `Parameters` as in assert  
## Returns​
`Ts`[]
## Example​
```typescript
fc.sample(fc.nat(), 10); // extract 10 values from fc.nat() Arbitrary  
fc.sample(fc.nat(), {seed: 42}); // extract values from fc.nat() as if we were running fc.assert with seed=42  
```
## Remarks​
Since 0.0.6
```

--------------------------------

### Generate Boolean Values

Source: https://fast-check.dev/docs/core-blocks/arbitraries/primitives/boolean

Use `fc.boolean()` to generate random boolean values. Examples include `true` and `false`.

```javascript
fc.boolean();  

// Examples of generated values: true, false…
```

--------------------------------

### Run Tests with npm

Source: https://fast-check.dev/docs/tutorials/quick-start/basic-setup

Execute the project's tests using the npm test script.

```bash
npm test  

```

--------------------------------

### Root package.json for Dual Module Support

Source: https://fast-check.dev/blog/2023/09/04/dual-packages-or-supporting-both-cjs-and-esm

Configure the root package.json with 'main' for CJS, 'module' for ESM, and the 'exports' field to define entry points for both module systems, including type definitions.

```json
{
  "type": "commonjs",
  "main": "lib/fast-check.js",
  "module": "lib/esm/fast-check.js",
  "exports": {
    "./package.json": "./package.json",
    ".": {
      "require": {
        "types": "./lib/fast-check.d.ts",
        "default": "./lib/fast-check.js"
      },
      "import": {
        "types": "./lib/esm/fast-check.d.ts",
        "default": "./lib/esm/fast-check.js"
      }
    }
  },
  "types": "lib/fast-check.d.ts"
}
```

--------------------------------

### Jest Configuration for Global Settings

Source: https://fast-check.dev/docs/configuration/global-settings

Configure Jest to load global settings by specifying a setup file in `jest.config.js`.

```javascript
module.exports = {
  setupFiles: ['./jest.setup.js'],
};
```

--------------------------------

### Map Arbitrary to Square Values

Source: https://fast-check.dev/docs/core-blocks/arbitraries/combiners/any

Use .map to transform generated values. This example maps natural numbers to their squares.

```javascript
fc.nat(1024).map((n) => n * n);
```

--------------------------------

### Generate ULID using fast-check

Source: https://fast-check.dev/blog/2023/06/07/whats-new-in-fast-check-3-11-0

Use the `ulid` arbitrary to generate ULID strings. Examples of generated values are provided.

```javascript
fc.ulid();  

// Examples of generated values:  

// • "7AVDFZJAXCM0F25E3SZZZZZZYZ"  

// • "7ZZZZZZZYP5XN60H51ZZZZZZZP"  

// • "2VXXEMQ2HWRSNWMP9PZZZZZZZA"  

// • "15RQ23H1M8YB80EVPD2EG8W7K1"  

// • "6QV4RKC7C8ZZZZZZZFSF7PWQF5"  

// • …  
```

--------------------------------

### modelRun()

Source: https://fast-check.dev/docs/api/functions/modelRun

Runs synchronous commands over a Model and the Real system. Throws in case of inconsistency.

```APIDOC
## Function: modelRun()

> **modelRun** <`Model`, `Real`, `InitialModel`>(`s`, `cmds`): `void`

Defined in: packages/fast-check/src/check/model/ModelRunner.ts:113

Run synchronous commands over a `Model` and the `Real` system
Throw in case of inconsistency

## Type Parameters

| Type Parameter  | Description |
|---|---|
| `Model` _extends_ `object`  |
| `Real`  |
| `InitialModel` _extends_ `object`  |

## Parameters

| Parameter | Type | Description |
|---|---|---|
| `s` | `ModelRunSetup`<`InitialModel`, `Real`> | Initial state provider |
| `cmds` | `Iterable`<`Command`<`Model`, `Real`>> | Synchronous commands to be executed |

## Returns

`void`

## Remarks

Since 1.5.0
```

--------------------------------

### Map Arbitrary to String Type

Source: https://fast-check.dev/docs/core-blocks/arbitraries/combiners/any

Transform the type of generated values using .map. This example converts natural numbers to strings.

```javascript
fc.nat().map((n) => String(n));
```

--------------------------------

### asyncProperty()

Source: https://fast-check.dev/docs/api/functions/asyncProperty

Instantiate a new fast-check#IAsyncProperty.

```APIDOC
## Function: asyncProperty()

> **asyncProperty** <`Ts`>(...`args`): `IAsyncPropertyWithHooks`<`Ts`>

Defined in: packages/fast-check/src/check/property/AsyncProperty.ts:15

Instantiate a new fast-check#IAsyncProperty.

## Type Parameters​

Type Parameter  
---
`Ts` _extends_ [`unknown`, `...unknown[]`]

## Parameters​

Parameter| Type  
--|--
...`args`| [...arbitraries: { [K in string | number | symbol]: Arbitrary<Ts[K]> }[], (...`args`) => `Promise`<`boolean` | `void`>]

## Returns​

`IAsyncPropertyWithHooks`<`Ts`>

## Remarks​

Since 0.0.7
```

--------------------------------

### Random User Test

Source: https://fast-check.dev/docs/advanced/fake-data

Example of a traditional random test generating user data. This approach lacks reproducibility and shrinking capabilities.

```javascript
test('sort users by ascending age', () => {
  const userA = {
    firstName: firstName(),
    lastName: lastName(),
    birthDate: birthDate(),
  };
  const userB = {
    firstName: firstName(),
    lastName: lastName(),
    birthDate: birthDate({ strictlyOlderThan: userA.birthDate }),
  };
  expect(sortByAge([userA, userB])).toEqual([userA, userB]);
  expect(sortByAge([userB, userA])).toEqual([userA, userB]);
});

```

--------------------------------

### anything(constraints)

Source: https://fast-check.dev/docs/api/functions/anything

Generates arbitrary values of any type following the specified constraints. You can use sample() to preview the generated values.

```APIDOC
## anything(constraints)

### Description
Generates arbitrary values of any type following the constraints defined by `settings`.

### Parameters
#### Parameters
- **constraints** (`ObjectConstraints`) - Constraints to apply when building instances

### Returns
`Arbitrary<unknown>`

### Examples
```
// Using custom settings

fc.anything({

    key: fc.string(),

    values: [fc.integer(10,20), fc.constant(42)],

    maxDepth: 2

});

// Can build entries such as:

// - 19

// - [{"2":12,"k":15,"A":42}]

// - {"4":[19,13,14,14,42,11,20,11],"6":42,"7":16,"L":10,"'":[20,11],"e":[42,20,42,14,13,17]}

// - [42,42,42]...
```

### Remarks
Since 0.0.7
```

--------------------------------

### Example Test Failure Report

Source: https://fast-check.dev/docs/tutorials/quick-start/read-test-reports

A typical test failure report from fast-check, indicating a property failure with a specific seed, path, and counterexample.

```text
**FAIL**  sort.test.mjs > should sort numeric elements from the smallest to the largest one  

Error: Property failed after 1 tests  

{ seed: -1819918769, path: "0:...:3", endOnFailure: true }  

Counterexample: [[2,1000000000]]  

Shrunk 66 time(s)  

Got error: AssertionError: expected 1000000000 to be less than or equal to 2  
```

--------------------------------

### Generate Tuple with Multiple Arbitraries

Source: https://fast-check.dev/docs/core-blocks/arbitraries/composites/array

Use fc.tuple with multiple arbitraries to generate arrays with elements corresponding to each arbitrary. Examples show generated values.

```javascript
fc.tuple(fc.nat(), fc.string());  

// Examples of generated values: [17,"n"], [1187149108,"{}"], [302474255,"!!]"], [2147483618,"$"], [21,"lv V!""]…
```

--------------------------------

### Basic fast-check property test

Source: https://fast-check.dev/docs/introduction/getting-started

Demonstrates how to import fast-check and define simple properties for testing. The `fc.assert` runner executes the property, attempting to shrink failures to minimal examples.

```javascript
import fc from 'fast-check';

// Code under test
const contains = (text, pattern) => text.indexOf(pattern) >= 0;

// Properties
describe('properties', () => {
  // string text always contains itself
  it('should always contain itself', () => {
    fc.assert(
      fc.property(fc.string(), (text) => {
        return contains(text, text);
      }),
    );
  });
  
  // string a + b + c always contains b, whatever the values of a, b and c
  it('should always contain its substrings', () => {
    fc.assert(
      fc.property(fc.string(), fc.string(), fc.string(), (a, b, c) => {
        // Alternatively: no return statement and direct usage of expect or assert
        return contains(a + b + c, b);
      }),
    );
  });
});

```

--------------------------------

### Generate Tuple with Single Arbitrary

Source: https://fast-check.dev/docs/core-blocks/arbitraries/composites/array

Use fc.tuple with a single arbitrary to generate arrays containing one element. Examples show generated values.

```javascript
fc.tuple(fc.nat());  

// Examples of generated values: [15], [1564085383], [2147483642], [1564562962], [891386821]…
```

--------------------------------

### Map String to Formatted String

Source: https://fast-check.dev/docs/core-blocks/arbitraries/combiners/any

Transform a generated string into a new formatted string using .map. This example prepends the string's length.

```javascript
fc.string().map((s) => `[${s.length}] -> ${s}`);
```