Source Code: lib/assert.js
\nThe assert module provides a set of assertion functions for verifying\ninvariants.
In strict assertion mode, non-strict methods behave like their corresponding\nstrict methods. For example, assert.deepEqual() will behave like\nassert.deepStrictEqual().
In strict assertion mode, error messages for objects display a diff. In legacy\nassertion mode, error messages for objects display the objects, often truncated.
\nTo use strict assertion mode:
\nconst assert = require('assert').strict;\nExample error diff:
\nconst assert = require('assert').strict;\n\nassert.deepEqual([[[1, 2, 3]], 4, 5], [[[1, 2, '3']], 4, 5]);\n// AssertionError: Expected inputs to be strictly deep-equal:\n// + actual - expected ... Lines skipped\n//\n// [\n// [\n// ...\n// 2,\n// + 3\n// - '3'\n// ],\n// ...\n// 5\n// ]\nTo deactivate the colors, use the NO_COLOR or NODE_DISABLE_COLORS\nenvironment variables. This will also deactivate the colors in the REPL. For\nmore on color support in terminal environments, read the tty\ngetColorDepth() documentation.
Legacy assertion mode uses the Abstract Equality Comparison in:
\n\nTo use legacy assertion mode:
\nconst assert = require('assert');\nWhenever possible, use the strict assertion mode instead. Otherwise, the\nAbstract Equality Comparison may cause surprising results. This is\nespecially true for assert.deepEqual(), where the comparison rules are\nlax:
// WARNING: This does not throw an AssertionError!\nassert.deepEqual(/a/gi, new Date());\nIndicates the failure of an assertion. All errors thrown by the assert module\nwill be instances of the AssertionError class.
A subclass of Error that indicates the failure of an assertion.
All instances contain the built-in Error properties (message and name)\nand:
actual <any> Set to the actual argument for methods such as\nassert.strictEqual().expected <any> Set to the expected value for methods such as\nassert.strictEqual().generatedMessage <boolean> Indicates if the message was auto-generated\n(true) or not.code <string> Value is always ERR_ASSERTION to show that the error is an\nassertion error.operator <string> Set to the passed in operator value.const assert = require('assert');\n\n// Generate an AssertionError to compare the error message later:\nconst { message } = new assert.AssertionError({\n actual: 1,\n expected: 2,\n operator: 'strictEqual'\n});\n\n// Verify error output:\ntry {\n assert.strictEqual(1, 2);\n} catch (err) {\n assert(err instanceof assert.AssertionError);\n assert.strictEqual(err.message, message);\n assert.strictEqual(err.name, 'AssertionError');\n assert.strictEqual(err.actual, 1);\n assert.strictEqual(err.expected, 2);\n assert.strictEqual(err.code, 'ERR_ASSERTION');\n assert.strictEqual(err.operator, 'strictEqual');\n assert.strictEqual(err.generatedMessage, true);\n}\nThis feature is currently experimental and behavior might still change.
", "methods": [ { "textRaw": "`tracker.calls([fn][, exact])`", "type": "method", "name": "calls", "meta": { "added": [ "v14.2.0" ], "changes": [] }, "signatures": [ { "return": { "textRaw": "Returns: {Function} that wraps `fn`.", "name": "return", "type": "Function", "desc": "that wraps `fn`." }, "params": [ { "textRaw": "`fn` {Function} **Default** A no-op function.", "name": "fn", "type": "Function", "desc": "**Default** A no-op function." }, { "textRaw": "`exact` {number} **Default** `1`.", "name": "exact", "type": "number", "desc": "**Default** `1`." } ] } ], "desc": "The wrapper function is expected to be called exactly exact times. If the\nfunction has not been called exactly exact times when\ntracker.verify() is called, then tracker.verify() will throw an\nerror.
const assert = require('assert');\n\n// Creates call tracker.\nconst tracker = new assert.CallTracker();\n\nfunction func() {}\n\n// Returns a function that wraps func() that must be called exact times\n// before tracker.verify().\nconst callsfunc = tracker.calls(func);\nThe arrays contains information about the expected and actual number of calls of\nthe functions that have not been called the expected number of times.
\nconst assert = require('assert');\n\n// Creates call tracker.\nconst tracker = new assert.CallTracker();\n\nfunction func() {}\n\nfunction foo() {}\n\n// Returns a function that wraps func() that must be called exact times\n// before tracker.verify().\nconst callsfunc = tracker.calls(func, 2);\n\n// Returns an array containing information on callsfunc()\ntracker.report();\n// [\n// {\n// message: 'Expected the func function to be executed 2 time(s) but was\n// executed 0 time(s).',\n// actual: 0,\n// expected: 2,\n// operator: 'func',\n// stack: stack trace\n// }\n// ]\nIterates through the list of functions passed to\ntracker.calls() and will throw an error for functions that\nhave not been called the expected number of times.
const assert = require('assert');\n\n// Creates call tracker.\nconst tracker = new assert.CallTracker();\n\nfunction func() {}\n\n// Returns a function that wraps func() that must be called exact times\n// before tracker.verify().\nconst callsfunc = tracker.calls(func, 2);\n\ncallsfunc();\n\n// Will throw an error since callsfunc() was only called once.\ntracker.verify();\nCreates a new CallTracker object which can be used to track if functions\nwere called a specific number of times. The tracker.verify() must be called\nfor the verification to take place. The usual pattern would be to call it in a\nprocess.on('exit') handler.
const assert = require('assert');\n\nconst tracker = new assert.CallTracker();\n\nfunction func() {}\n\n// callsfunc() must be called exactly 1 time before tracker.verify().\nconst callsfunc = tracker.calls(func, 1);\n\ncallsfunc();\n\n// Calls tracker.verify() and verifies if all tracker.calls() functions have\n// been called exact times.\nprocess.on('exit', () => {\n tracker.verify();\n});\nAn alias of assert.ok().
Strict assertion mode
\nAn alias of assert.deepStrictEqual().
Legacy assertion mode
\n\n\nStability: 3 - Legacy: Use
\nassert.deepStrictEqual()instead.
Tests for deep equality between the actual and expected parameters. Consider\nusing assert.deepStrictEqual() instead. assert.deepEqual() can have\nsurprising results.
Deep equality means that the enumerable \"own\" properties of child objects\nare also recursively evaluated by the following rules.
", "modules": [ { "textRaw": "Comparison details", "name": "comparison_details", "desc": "== ) with the exception of NaN. It is treated as being identical in case\nboth sides are NaN.Error names and messages are always compared, even if these are not\nenumerable properties.Object properties are compared unordered.Map keys and Set items are compared unordered.[[Prototype]] of\nobjects.Symbol properties are not compared.WeakMap and WeakSet comparison does not rely on their values.The following example does not throw an AssertionError because the\nprimitives are considered equal by the Abstract Equality Comparison\n( == ).
// WARNING: This does not throw an AssertionError!\nassert.deepEqual('+00000000', false);\n\"Deep\" equality means that the enumerable \"own\" properties of child objects\nare evaluated also:
\nconst assert = require('assert');\n\nconst obj1 = {\n a: {\n b: 1\n }\n};\nconst obj2 = {\n a: {\n b: 2\n }\n};\nconst obj3 = {\n a: {\n b: 1\n }\n};\nconst obj4 = Object.create(obj1);\n\nassert.deepEqual(obj1, obj1);\n// OK\n\n// Values of b are different:\nassert.deepEqual(obj1, obj2);\n// AssertionError: { a: { b: 1 } } deepEqual { a: { b: 2 } }\n\nassert.deepEqual(obj1, obj3);\n// OK\n\n// Prototypes are ignored:\nassert.deepEqual(obj1, obj4);\n// AssertionError: { a: { b: 1 } } deepEqual {}\nIf the values are not equal, an AssertionError is thrown with a message\nproperty set equal to the value of the message parameter. If the message\nparameter is undefined, a default error message is assigned. If the message\nparameter is an instance of an Error then it will be thrown instead of the\nAssertionError.
Tests for deep equality between the actual and expected parameters.\n\"Deep\" equality means that the enumerable \"own\" properties of child objects\nare recursively evaluated also by the following rules.
Object.is().[[Prototype]] of objects are compared using\nthe Strict Equality Comparison.Error names and messages are always compared, even if these are not\nenumerable properties.Symbol properties are compared as well.Object properties are compared unordered.Map keys and Set items are compared unordered.WeakMap and WeakSet comparison does not rely on their values. See\nbelow for further details.const assert = require('assert').strict;\n\n// This fails because 1 !== '1'.\nassert.deepStrictEqual({ a: 1 }, { a: '1' });\n// AssertionError: Expected inputs to be strictly deep-equal:\n// + actual - expected\n//\n// {\n// + a: 1\n// - a: '1'\n// }\n\n// The following objects don't have own properties\nconst date = new Date();\nconst object = {};\nconst fakeDate = {};\nObject.setPrototypeOf(fakeDate, Date.prototype);\n\n// Different [[Prototype]]:\nassert.deepStrictEqual(object, fakeDate);\n// AssertionError: Expected inputs to be strictly deep-equal:\n// + actual - expected\n//\n// + {}\n// - Date {}\n\n// Different type tags:\nassert.deepStrictEqual(date, fakeDate);\n// AssertionError: Expected inputs to be strictly deep-equal:\n// + actual - expected\n//\n// + 2018-04-26T00:49:08.604Z\n// - Date {}\n\nassert.deepStrictEqual(NaN, NaN);\n// OK, because of the SameValue comparison\n\n// Different unwrapped numbers:\nassert.deepStrictEqual(new Number(1), new Number(2));\n// AssertionError: Expected inputs to be strictly deep-equal:\n// + actual - expected\n//\n// + [Number: 1]\n// - [Number: 2]\n\nassert.deepStrictEqual(new String('foo'), Object('foo'));\n// OK because the object and the string are identical when unwrapped.\n\nassert.deepStrictEqual(-0, -0);\n// OK\n\n// Different zeros using the SameValue Comparison:\nassert.deepStrictEqual(0, -0);\n// AssertionError: Expected inputs to be strictly deep-equal:\n// + actual - expected\n//\n// + 0\n// - -0\n\nconst symbol1 = Symbol();\nconst symbol2 = Symbol();\nassert.deepStrictEqual({ [symbol1]: 1 }, { [symbol1]: 1 });\n// OK, because it is the same symbol on both objects.\n\nassert.deepStrictEqual({ [symbol1]: 1 }, { [symbol2]: 1 });\n// AssertionError [ERR_ASSERTION]: Inputs identical but not reference equal:\n//\n// {\n// [Symbol()]: 1\n// }\n\nconst weakMap1 = new WeakMap();\nconst weakMap2 = new WeakMap([[{}, {}]]);\nconst weakMap3 = new WeakMap();\nweakMap3.unequal = true;\n\nassert.deepStrictEqual(weakMap1, weakMap2);\n// OK, because it is impossible to compare the entries\n\n// Fails because weakMap3 has a property that weakMap1 does not contain:\nassert.deepStrictEqual(weakMap1, weakMap3);\n// AssertionError: Expected inputs to be strictly deep-equal:\n// + actual - expected\n//\n// WeakMap {\n// + [items unknown]\n// - [items unknown],\n// - unequal: true\n// }\nIf the values are not equal, an AssertionError is thrown with a message\nproperty set equal to the value of the message parameter. If the message\nparameter is undefined, a default error message is assigned. If the message\nparameter is an instance of an Error then it will be thrown instead of the\nAssertionError.
Expects the string input not to match the regular expression.
This feature is currently experimental and the name might change or it might be\ncompletely removed again.
\nconst assert = require('assert').strict;\n\nassert.doesNotMatch('I will fail', /fail/);\n// AssertionError [ERR_ASSERTION]: The input was expected to not match the ...\n\nassert.doesNotMatch(123, /pass/);\n// AssertionError [ERR_ASSERTION]: The \"string\" argument must be of type string.\n\nassert.doesNotMatch('I will pass', /different/);\n// OK\nIf the values do match, or if the string argument is of another type than\nstring, an AssertionError is thrown with a message property set equal\nto the value of the message parameter. If the message parameter is\nundefined, a default error message is assigned. If the message parameter is an\ninstance of an Error then it will be thrown instead of the\nAssertionError.
Awaits the asyncFn promise or, if asyncFn is a function, immediately\ncalls the function and awaits the returned promise to complete. It will then\ncheck that the promise is not rejected.
If asyncFn is a function and it throws an error synchronously,\nassert.doesNotReject() will return a rejected Promise with that error. If\nthe function does not return a promise, assert.doesNotReject() will return a\nrejected Promise with an ERR_INVALID_RETURN_VALUE error. In both cases\nthe error handler is skipped.
Using assert.doesNotReject() is actually not useful because there is little\nbenefit in catching a rejection and then rejecting it again. Instead, consider\nadding a comment next to the specific code path that should not reject and keep\nerror messages as expressive as possible.
If specified, error can be a Class, RegExp or a validation\nfunction. See assert.throws() for more details.
Besides the async nature to await the completion behaves identically to\nassert.doesNotThrow().
(async () => {\n await assert.doesNotReject(\n async () => {\n throw new TypeError('Wrong value');\n },\n SyntaxError\n );\n})();\nassert.doesNotReject(Promise.reject(new TypeError('Wrong value')))\n .then(() => {\n // ...\n });\nAsserts that the function fn does not throw an error.
Using assert.doesNotThrow() is actually not useful because there\nis no benefit in catching an error and then rethrowing it. Instead, consider\nadding a comment next to the specific code path that should not throw and keep\nerror messages as expressive as possible.
When assert.doesNotThrow() is called, it will immediately call the fn\nfunction.
If an error is thrown and it is the same type as that specified by the error\nparameter, then an AssertionError is thrown. If the error is of a\ndifferent type, or if the error parameter is undefined, the error is\npropagated back to the caller.
If specified, error can be a Class, RegExp or a validation\nfunction. See assert.throws() for more details.
The following, for instance, will throw the TypeError because there is no\nmatching error type in the assertion:
assert.doesNotThrow(\n () => {\n throw new TypeError('Wrong value');\n },\n SyntaxError\n);\nHowever, the following will result in an AssertionError with the message\n'Got unwanted exception...':
assert.doesNotThrow(\n () => {\n throw new TypeError('Wrong value');\n },\n TypeError\n);\nIf an AssertionError is thrown and a value is provided for the message\nparameter, the value of message will be appended to the AssertionError\nmessage:
assert.doesNotThrow(\n () => {\n throw new TypeError('Wrong value');\n },\n /Wrong value/,\n 'Whoops'\n);\n// Throws: AssertionError: Got unwanted exception: Whoops\nStrict assertion mode
\nAn alias of assert.strictEqual().
Legacy assertion mode
\n\n\nStability: 3 - Legacy: Use
\nassert.strictEqual()instead.
Tests shallow, coercive equality between the actual and expected parameters\nusing the Abstract Equality Comparison ( == ). NaN is special handled\nand treated as being identical in case both sides are NaN.
const assert = require('assert');\n\nassert.equal(1, 1);\n// OK, 1 == 1\nassert.equal(1, '1');\n// OK, 1 == '1'\nassert.equal(NaN, NaN);\n// OK\n\nassert.equal(1, 2);\n// AssertionError: 1 == 2\nassert.equal({ a: { b: 1 } }, { a: { b: 1 } });\n// AssertionError: { a: { b: 1 } } == { a: { b: 1 } }\nIf the values are not equal, an AssertionError is thrown with a message\nproperty set equal to the value of the message parameter. If the message\nparameter is undefined, a default error message is assigned. If the message\nparameter is an instance of an Error then it will be thrown instead of the\nAssertionError.
Throws an AssertionError with the provided error message or a default\nerror message. If the message parameter is an instance of an Error then\nit will be thrown instead of the AssertionError.
const assert = require('assert').strict;\n\nassert.fail();\n// AssertionError [ERR_ASSERTION]: Failed\n\nassert.fail('boom');\n// AssertionError [ERR_ASSERTION]: boom\n\nassert.fail(new TypeError('need array'));\n// TypeError: need array\nUsing assert.fail() with more than two arguments is possible but deprecated.\nSee below for further details.
If message is falsy, the error message is set as the values of actual and\nexpected separated by the provided operator. If just the two actual and\nexpected arguments are provided, operator will default to '!='. If\nmessage is provided as third argument it will be used as the error message and\nthe other arguments will be stored as properties on the thrown object. If\nstackStartFn is provided, all stack frames above that function will be\nremoved from stacktrace (see Error.captureStackTrace). If no arguments are\ngiven, the default message Failed will be used.
const assert = require('assert').strict;\n\nassert.fail('a', 'b');\n// AssertionError [ERR_ASSERTION]: 'a' != 'b'\n\nassert.fail(1, 2, undefined, '>');\n// AssertionError [ERR_ASSERTION]: 1 > 2\n\nassert.fail(1, 2, 'fail');\n// AssertionError [ERR_ASSERTION]: fail\n\nassert.fail(1, 2, 'whoops', '>');\n// AssertionError [ERR_ASSERTION]: whoops\n\nassert.fail(1, 2, new TypeError('need array'));\n// TypeError: need array\nIn the last three cases actual, expected, and operator have no\ninfluence on the error message.
Example use of stackStartFn for truncating the exception's stacktrace:
function suppressFrame() {\n assert.fail('a', 'b', undefined, '!==', suppressFrame);\n}\nsuppressFrame();\n// AssertionError [ERR_ASSERTION]: 'a' !== 'b'\n// at repl:1:1\n// at ContextifyScript.Script.runInThisContext (vm.js:44:33)\n// ...\nThrows value if value is not undefined or null. This is useful when\ntesting the error argument in callbacks. The stack trace contains all frames\nfrom the error passed to ifError() including the potential new frames for\nifError() itself.
const assert = require('assert').strict;\n\nassert.ifError(null);\n// OK\nassert.ifError(0);\n// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: 0\nassert.ifError('error');\n// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: 'error'\nassert.ifError(new Error());\n// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: Error\n\n// Create some random error frames.\nlet err;\n(function errorFrame() {\n err = new Error('test error');\n})();\n\n(function ifErrorFrame() {\n assert.ifError(err);\n})();\n// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: test error\n// at ifErrorFrame\n// at errorFrame\nExpects the string input to match the regular expression.
This feature is currently experimental and the name might change or it might be\ncompletely removed again.
\nconst assert = require('assert').strict;\n\nassert.match('I will fail', /pass/);\n// AssertionError [ERR_ASSERTION]: The input did not match the regular ...\n\nassert.match(123, /pass/);\n// AssertionError [ERR_ASSERTION]: The \"string\" argument must be of type string.\n\nassert.match('I will pass', /pass/);\n// OK\nIf the values do not match, or if the string argument is of another type than\nstring, an AssertionError is thrown with a message property set equal\nto the value of the message parameter. If the message parameter is\nundefined, a default error message is assigned. If the message parameter is an\ninstance of an Error then it will be thrown instead of the\nAssertionError.
Strict assertion mode
\nAn alias of assert.notDeepStrictEqual().
Legacy assertion mode
\n\n\nStability: 3 - Legacy: Use
\nassert.notDeepStrictEqual()instead.
Tests for any deep inequality. Opposite of assert.deepEqual().
const assert = require('assert');\n\nconst obj1 = {\n a: {\n b: 1\n }\n};\nconst obj2 = {\n a: {\n b: 2\n }\n};\nconst obj3 = {\n a: {\n b: 1\n }\n};\nconst obj4 = Object.create(obj1);\n\nassert.notDeepEqual(obj1, obj1);\n// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }\n\nassert.notDeepEqual(obj1, obj2);\n// OK\n\nassert.notDeepEqual(obj1, obj3);\n// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }\n\nassert.notDeepEqual(obj1, obj4);\n// OK\nIf the values are deeply equal, an AssertionError is thrown with a\nmessage property set equal to the value of the message parameter. If the\nmessage parameter is undefined, a default error message is assigned. If the\nmessage parameter is an instance of an Error then it will be thrown\ninstead of the AssertionError.
Tests for deep strict inequality. Opposite of assert.deepStrictEqual().
const assert = require('assert').strict;\n\nassert.notDeepStrictEqual({ a: 1 }, { a: '1' });\n// OK\nIf the values are deeply and strictly equal, an AssertionError is thrown\nwith a message property set equal to the value of the message parameter. If\nthe message parameter is undefined, a default error message is assigned. If\nthe message parameter is an instance of an Error then it will be thrown\ninstead of the AssertionError.
Strict assertion mode
\nAn alias of assert.notStrictEqual().
Legacy assertion mode
\n\n\nStability: 3 - Legacy: Use
\nassert.notStrictEqual()instead.
Tests shallow, coercive inequality with the Abstract Equality Comparison\n(!= ). NaN is special handled and treated as being identical in case both\nsides are NaN.
const assert = require('assert');\n\nassert.notEqual(1, 2);\n// OK\n\nassert.notEqual(1, 1);\n// AssertionError: 1 != 1\n\nassert.notEqual(1, '1');\n// AssertionError: 1 != '1'\nIf the values are equal, an AssertionError is thrown with a message\nproperty set equal to the value of the message parameter. If the message\nparameter is undefined, a default error message is assigned. If the message\nparameter is an instance of an Error then it will be thrown instead of the\nAssertionError.
Tests strict inequality between the actual and expected parameters as\ndetermined by the SameValue Comparison.
const assert = require('assert').strict;\n\nassert.notStrictEqual(1, 2);\n// OK\n\nassert.notStrictEqual(1, 1);\n// AssertionError [ERR_ASSERTION]: Expected \"actual\" to be strictly unequal to:\n//\n// 1\n\nassert.notStrictEqual(1, '1');\n// OK\nIf the values are strictly equal, an AssertionError is thrown with a\nmessage property set equal to the value of the message parameter. If the\nmessage parameter is undefined, a default error message is assigned. If the\nmessage parameter is an instance of an Error then it will be thrown\ninstead of the AssertionError.
Tests if value is truthy. It is equivalent to\nassert.equal(!!value, true, message).
If value is not truthy, an AssertionError is thrown with a message\nproperty set equal to the value of the message parameter. If the message\nparameter is undefined, a default error message is assigned. If the message\nparameter is an instance of an Error then it will be thrown instead of the\nAssertionError.\nIf no arguments are passed in at all message will be set to the string:\n'No value argument passed to `assert.ok()`'.
Be aware that in the repl the error message will be different to the one\nthrown in a file! See below for further details.
const assert = require('assert').strict;\n\nassert.ok(true);\n// OK\nassert.ok(1);\n// OK\n\nassert.ok();\n// AssertionError: No value argument passed to `assert.ok()`\n\nassert.ok(false, 'it\\'s false');\n// AssertionError: it's false\n\n// In the repl:\nassert.ok(typeof 123 === 'string');\n// AssertionError: false == true\n\n// In a file (e.g. test.js):\nassert.ok(typeof 123 === 'string');\n// AssertionError: The expression evaluated to a falsy value:\n//\n// assert.ok(typeof 123 === 'string')\n\nassert.ok(false);\n// AssertionError: The expression evaluated to a falsy value:\n//\n// assert.ok(false)\n\nassert.ok(0);\n// AssertionError: The expression evaluated to a falsy value:\n//\n// assert.ok(0)\n\n// Using `assert()` works the same:\nassert(0);\n// AssertionError: The expression evaluated to a falsy value:\n//\n// assert(0)\nAwaits the asyncFn promise or, if asyncFn is a function, immediately\ncalls the function and awaits the returned promise to complete. It will then\ncheck that the promise is rejected.
If asyncFn is a function and it throws an error synchronously,\nassert.rejects() will return a rejected Promise with that error. If the\nfunction does not return a promise, assert.rejects() will return a rejected\nPromise with an ERR_INVALID_RETURN_VALUE error. In both cases the error\nhandler is skipped.
Besides the async nature to await the completion behaves identically to\nassert.throws().
If specified, error can be a Class, RegExp, a validation function,\nan object where each property will be tested for, or an instance of error where\neach property will be tested for including the non-enumerable message and\nname properties.
If specified, message will be the message provided by the AssertionError\nif the asyncFn fails to reject.
(async () => {\n await assert.rejects(\n async () => {\n throw new TypeError('Wrong value');\n },\n {\n name: 'TypeError',\n message: 'Wrong value'\n }\n );\n})();\n(async () => {\n await assert.rejects(\n async () => {\n throw new TypeError('Wrong value');\n },\n (err) => {\n assert.strictEqual(err.name, 'TypeError');\n assert.strictEqual(err.message, 'Wrong value');\n return true;\n }\n );\n})();\nassert.rejects(\n Promise.reject(new Error('Wrong value')),\n Error\n).then(() => {\n // ...\n});\nerror cannot be a string. If a string is provided as the second\nargument, then error is assumed to be omitted and the string will be used for\nmessage instead. This can lead to easy-to-miss mistakes. Please read the\nexample in assert.throws() carefully if using a string as the second\nargument gets considered.
Tests strict equality between the actual and expected parameters as\ndetermined by the SameValue Comparison.
const assert = require('assert').strict;\n\nassert.strictEqual(1, 2);\n// AssertionError [ERR_ASSERTION]: Expected inputs to be strictly equal:\n//\n// 1 !== 2\n\nassert.strictEqual(1, 1);\n// OK\n\nassert.strictEqual('Hello foobar', 'Hello World!');\n// AssertionError [ERR_ASSERTION]: Expected inputs to be strictly equal:\n// + actual - expected\n//\n// + 'Hello foobar'\n// - 'Hello World!'\n// ^\n\nconst apples = 1;\nconst oranges = 2;\nassert.strictEqual(apples, oranges, `apples ${apples} !== oranges ${oranges}`);\n// AssertionError [ERR_ASSERTION]: apples 1 !== oranges 2\n\nassert.strictEqual(1, '1', new TypeError('Inputs are not identical'));\n// TypeError: Inputs are not identical\nIf the values are not strictly equal, an AssertionError is thrown with a\nmessage property set equal to the value of the message parameter. If the\nmessage parameter is undefined, a default error message is assigned. If the\nmessage parameter is an instance of an Error then it will be thrown\ninstead of the AssertionError.
Expects the function fn to throw an error.
If specified, error can be a Class, RegExp, a validation function,\na validation object where each property will be tested for strict deep equality,\nor an instance of error where each property will be tested for strict deep\nequality including the non-enumerable message and name properties. When\nusing an object, it is also possible to use a regular expression, when\nvalidating against a string property. See below for examples.
If specified, message will be appended to the message provided by the\nAssertionError if the fn call fails to throw or in case the error validation\nfails.
Custom validation object/error instance:
\nconst err = new TypeError('Wrong value');\nerr.code = 404;\nerr.foo = 'bar';\nerr.info = {\n nested: true,\n baz: 'text'\n};\nerr.reg = /abc/i;\n\nassert.throws(\n () => {\n throw err;\n },\n {\n name: 'TypeError',\n message: 'Wrong value',\n info: {\n nested: true,\n baz: 'text'\n }\n // Only properties on the validation object will be tested for.\n // Using nested objects requires all properties to be present. Otherwise\n // the validation is going to fail.\n }\n);\n\n// Using regular expressions to validate error properties:\nassert.throws(\n () => {\n throw err;\n },\n {\n // The `name` and `message` properties are strings and using regular\n // expressions on those will match against the string. If they fail, an\n // error is thrown.\n name: /^TypeError$/,\n message: /Wrong/,\n foo: 'bar',\n info: {\n nested: true,\n // It is not possible to use regular expressions for nested properties!\n baz: 'text'\n },\n // The `reg` property contains a regular expression and only if the\n // validation object contains an identical regular expression, it is going\n // to pass.\n reg: /abc/i\n }\n);\n\n// Fails due to the different `message` and `name` properties:\nassert.throws(\n () => {\n const otherErr = new Error('Not found');\n // Copy all enumerable properties from `err` to `otherErr`.\n for (const [key, value] of Object.entries(err)) {\n otherErr[key] = value;\n }\n throw otherErr;\n },\n // The error's `message` and `name` properties will also be checked when using\n // an error as validation object.\n err\n);\nValidate instanceof using constructor:
\nassert.throws(\n () => {\n throw new Error('Wrong value');\n },\n Error\n);\nValidate error message using RegExp:
Using a regular expression runs .toString on the error object, and will\ntherefore also include the error name.
assert.throws(\n () => {\n throw new Error('Wrong value');\n },\n /^Error: Wrong value$/\n);\nCustom error validation:
\nThe function must return true to indicate all internal validations passed.\nIt will otherwise fail with an AssertionError.
assert.throws(\n () => {\n throw new Error('Wrong value');\n },\n (err) => {\n assert(err instanceof Error);\n assert(/value/.test(err));\n // Avoid returning anything from validation functions besides `true`.\n // Otherwise, it's not clear what part of the validation failed. Instead,\n // throw an error about the specific validation that failed (as done in this\n // example) and add as much helpful debugging information to that error as\n // possible.\n return true;\n },\n 'unexpected error'\n);\nerror cannot be a string. If a string is provided as the second\nargument, then error is assumed to be omitted and the string will be used for\nmessage instead. This can lead to easy-to-miss mistakes. Using the same\nmessage as the thrown error message is going to result in an\nERR_AMBIGUOUS_ARGUMENT error. Please read the example below carefully if using\na string as the second argument gets considered:
function throwingFirst() {\n throw new Error('First');\n}\n\nfunction throwingSecond() {\n throw new Error('Second');\n}\n\nfunction notThrowing() {}\n\n// The second argument is a string and the input function threw an Error.\n// The first case will not throw as it does not match for the error message\n// thrown by the input function!\nassert.throws(throwingFirst, 'Second');\n// In the next example the message has no benefit over the message from the\n// error and since it is not clear if the user intended to actually match\n// against the error message, Node.js throws an `ERR_AMBIGUOUS_ARGUMENT` error.\nassert.throws(throwingSecond, 'Second');\n// TypeError [ERR_AMBIGUOUS_ARGUMENT]\n\n// The string is only used (as message) in case the function does not throw:\nassert.throws(notThrowing, 'Second');\n// AssertionError [ERR_ASSERTION]: Missing expected exception: Second\n\n// If it was intended to match for the error message do this instead:\n// It does not throw because the error messages match.\nassert.throws(throwingSecond, /Second$/);\n\n// If the error message does not match, an AssertionError is thrown.\nassert.throws(throwingFirst, /Second$/);\n// AssertionError [ERR_ASSERTION]\nDue to the confusing error-prone notation, avoid a string as the second\nargument.
" } ], "type": "module", "displayName": "Assert" } ] }