{ "source": "doc/api/assert.md", "modules": [ { "textRaw": "Assert", "name": "assert", "introduced_in": "v0.10.0", "stability": 2, "stabilityText": "Stable", "desc": "
The assert
module provides a simple set of assertion tests that can be used to\ntest invariants.
An alias of assert.ok()
.
Tests for deep equality between the actual
and expected
parameters.\nPrimitive values are compared with the Abstract Equality Comparison\n( ==
).
Only enumerable "own" properties are considered. The\nassert.deepEqual()
implementation does not test the\n[[Prototype]]
of objects or enumerable own Symbol
\nproperties. For such checks, consider using assert.deepStrictEqual()
\ninstead. assert.deepEqual()
can have potentially surprising results. The\nfollowing example does not throw an AssertionError
because the properties on\nthe RegExp
object are not enumerable:
// WARNING: This does not throw an AssertionError!\nassert.deepEqual(/a/gi, new Date());\n
\nAn exception is made for Map
and Set
. Maps and Sets have their\ncontained items compared too, as expected.
"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, object is equal to itself\n\nassert.deepEqual(obj1, obj2);\n// AssertionError: { a: { b: 1 } } deepEqual { a: { b: 2 } }\n// values of b are different\n\nassert.deepEqual(obj1, obj3);\n// OK, objects are equal\n\nassert.deepEqual(obj1, obj4);\n// AssertionError: { a: { b: 1 } } deepEqual {}\n// Prototypes are ignored\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
.
Identical to assert.deepEqual()
with the following exceptions:
NaN
are compared using the Strict Equality\nComparison ( ===
). Set and Map values, Map keys and NaN
are compared\nusing the SameValueZero comparison (which means they are free of the\ncaveats).[[Prototype]]
of objects are compared using\nthe Strict Equality Comparison too.0
and -0
are not considered equal.Symbol
properties are compared as well.const assert = require('assert');\n\nassert.deepEqual({ a: 1 }, { a: '1' });\n// OK, because 1 == '1'\n\nassert.deepStrictEqual({ a: 1 }, { a: '1' });\n// AssertionError: { a: 1 } deepStrictEqual { a: '1' }\n// because 1 !== '1' using strict equality\n\n// The following objects don't have own properties\nconst date = new Date();\nconst object = {};\nconst fakeDate = {};\n\nObject.setPrototypeOf(fakeDate, Date.prototype);\n\nassert.deepEqual(object, fakeDate);\n// OK, doesn't check [[Prototype]]\nassert.deepStrictEqual(object, fakeDate);\n// AssertionError: {} deepStrictEqual Date {}\n// Different [[Prototype]]\n\nassert.deepEqual(date, fakeDate);\n// OK, doesn't check type tags\nassert.deepStrictEqual(date, fakeDate);\n// AssertionError: 2017-03-11T14:25:31.849Z deepStrictEqual Date {}\n// Different type tags\n\nassert.deepStrictEqual(NaN, NaN);\n// OK, because of the SameValueZero comparison\n\nassert.deepStrictEqual(new Number(1), new Number(2));\n// Fails because the wrapped number is unwrapped and compared as well.\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\nassert.deepStrictEqual(0, -0);\n// AssertionError: 0 deepStrictEqual -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.\nassert.deepStrictEqual({ [symbol1]: 1 }, { [symbol2]: 1 });\n// Fails because symbol1 !== symbol2!\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
.
Asserts that the function block
does not throw an error. See\nassert.throws()
for more details.
When assert.doesNotThrow()
is called, it will immediately call the block
\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 different\ntype, or if the error
parameter is undefined, the error is propagated back\nto the caller.
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);\n
\nHowever, the following will result in an AssertionError
with the message\n'Got unwanted exception (TypeError)..':
assert.doesNotThrow(\n () => {\n throw new TypeError('Wrong value');\n },\n TypeError\n);\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 TypeError,\n 'Whoops'\n);\n// Throws: AssertionError: Got unwanted exception (TypeError). Whoops\n
\n"
},
{
"textRaw": "assert.equal(actual, expected[, message])",
"type": "method",
"name": "equal",
"meta": {
"added": [
"v0.1.21"
],
"changes": []
},
"signatures": [
{
"params": [
{
"textRaw": "`actual` {any} ",
"name": "actual",
"type": "any"
},
{
"textRaw": "`expected` {any} ",
"name": "expected",
"type": "any"
},
{
"textRaw": "`message` {any} ",
"name": "message",
"type": "any",
"optional": true
}
]
},
{
"params": [
{
"name": "actual"
},
{
"name": "expected"
},
{
"name": "message",
"optional": true
}
]
}
],
"desc": "Tests shallow, coercive equality between the actual
and expected
parameters\nusing the Abstract Equality Comparison ( ==
).
const assert = require('assert');\n\nassert.equal(1, 1);\n// OK, 1 == 1\nassert.equal(1, '1');\n// OK, 1 == '1'\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 } }\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
.
Throws an AssertionError
. If message
is falsy, the error message is set as\nthe values of actual
and expected
separated by the provided operator
. If\nthe message
parameter is an instance of an Error
then it will be thrown\ninstead of the AssertionError
. If just the two actual
and expected
\narguments are provided, operator
will default to '!='
. If message
is\nprovided only it will be used as the error message, the other arguments will be\nstored as properties on the thrown object. If stackStartFunction
is provided,\nall stack frames above that function will be removed from stacktrace (see\nError.captureStackTrace
). If no arguments are given, the default message\nFailed
will be used.
const assert = require('assert');\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\n
\nNote: In the last two cases actual
, expected
, and operator
have no\ninfluence on the error message.
assert.fail();\n// AssertionError [ERR_ASSERTION]: Failed\n\nassert.fail('boom');\n// AssertionError [ERR_ASSERTION]: boom\n\nassert.fail('a', 'b');\n// AssertionError [ERR_ASSERTION]: 'a' != 'b'\n
\nExample use of stackStartFunction
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// ...\n
\n"
},
{
"textRaw": "assert.fail(actual, expected[, message[, operator[, stackStartFunction]]])",
"type": "method",
"name": "fail",
"meta": {
"added": [
"v0.1.21"
],
"changes": []
},
"signatures": [
{
"params": [
{
"textRaw": "`actual` {any} ",
"name": "actual",
"type": "any"
},
{
"textRaw": "`expected` {any} ",
"name": "expected",
"type": "any"
},
{
"textRaw": "`message` {any} **Default:** `'Failed'` ",
"name": "message",
"type": "any",
"desc": "**Default:** `'Failed'`",
"optional": true
},
{
"textRaw": "`operator` {string} **Default:** '!=' ",
"name": "operator",
"type": "string",
"desc": "**Default:** '!='",
"optional": true
},
{
"textRaw": "`stackStartFunction` {Function} **Default:** `assert.fail` ",
"name": "stackStartFunction",
"type": "Function",
"desc": "**Default:** `assert.fail`",
"optional": true
}
]
},
{
"params": [
{
"name": "actual"
},
{
"name": "expected"
},
{
"name": "message",
"optional": true
},
{
"name": "operator",
"optional": true
},
{
"name": "stackStartFunction",
"optional": true
}
]
}
],
"desc": "Throws an AssertionError
. If message
is falsy, the error message is set as\nthe values of actual
and expected
separated by the provided operator
. If\nthe message
parameter is an instance of an Error
then it will be thrown\ninstead of the AssertionError
. If just the two actual
and expected
\narguments are provided, operator
will default to '!='
. If message
is\nprovided only it will be used as the error message, the other arguments will be\nstored as properties on the thrown object. If stackStartFunction
is provided,\nall stack frames above that function will be removed from stacktrace (see\nError.captureStackTrace
). If no arguments are given, the default message\nFailed
will be used.
const assert = require('assert');\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\n
\nNote: In the last two cases actual
, expected
, and operator
have no\ninfluence on the error message.
assert.fail();\n// AssertionError [ERR_ASSERTION]: Failed\n\nassert.fail('boom');\n// AssertionError [ERR_ASSERTION]: boom\n\nassert.fail('a', 'b');\n// AssertionError [ERR_ASSERTION]: 'a' != 'b'\n
\nExample use of stackStartFunction
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// ...\n
\n"
},
{
"textRaw": "assert.ifError(value)",
"type": "method",
"name": "ifError",
"meta": {
"added": [
"v0.1.97"
],
"changes": []
},
"signatures": [
{
"params": [
{
"textRaw": "`value` {any} ",
"name": "value",
"type": "any"
}
]
},
{
"params": [
{
"name": "value"
}
]
}
],
"desc": "Throws value
if value
is truthy. This is useful when testing the error
\nargument in callbacks.
const assert = require('assert');\n\nassert.ifError(null);\n// OK\nassert.ifError(0);\n// OK\nassert.ifError(1);\n// Throws 1\nassert.ifError('error');\n// Throws 'error'\nassert.ifError(new Error());\n// Throws Error\n
\n"
},
{
"textRaw": "assert.notDeepEqual(actual, expected[, message])",
"type": "method",
"name": "notDeepEqual",
"meta": {
"added": [
"v0.1.21"
],
"changes": [
{
"version": "v9.0.0",
"pr-url": "https://github.com/nodejs/node/pull/15001",
"description": "Error names and messages are now properly compared"
},
{
"version": "v8.0.0",
"pr-url": "https://github.com/nodejs/node/pull/12142",
"description": "Set and Map content is also compared"
},
{
"version": "v6.4.0, v4.7.1",
"pr-url": "https://github.com/nodejs/node/pull/8002",
"description": "Typed array slices are handled correctly now."
},
{
"version": "v6.1.0, v4.5.0",
"pr-url": "https://github.com/nodejs/node/pull/6432",
"description": "Objects with circular references can be used as inputs now."
},
{
"version": "v5.10.1, v4.4.3",
"pr-url": "https://github.com/nodejs/node/pull/5910",
"description": "Handle non-`Uint8Array` typed arrays correctly."
}
]
},
"signatures": [
{
"params": [
{
"textRaw": "`actual` {any} ",
"name": "actual",
"type": "any"
},
{
"textRaw": "`expected` {any} ",
"name": "expected",
"type": "any"
},
{
"textRaw": "`message` {any} ",
"name": "message",
"type": "any",
"optional": true
}
]
},
{
"params": [
{
"name": "actual"
},
{
"name": "expected"
},
{
"name": "message",
"optional": true
}
]
}
],
"desc": "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: obj1 and obj2 are not deeply equal\n\nassert.notDeepEqual(obj1, obj3);\n// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }\n\nassert.notDeepEqual(obj1, obj4);\n// OK: obj1 and obj4 are not deeply equal\n
\nIf the values are deeply 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 strict inequality. Opposite of assert.deepStrictEqual()
.
const assert = require('assert');\n\nassert.notDeepEqual({ a: 1 }, { a: '1' });\n// AssertionError: { a: 1 } notDeepEqual { a: '1' }\n\nassert.notDeepStrictEqual({ a: 1 }, { a: '1' });\n// OK\n
\nIf the values are deeply and strictly equal, an AssertionError
is thrown with\na message
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 instead\nof the AssertionError
.
Tests shallow, coercive inequality with the Abstract Equality Comparison\n( !=
).
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'\n
\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 as determined by the Strict Equality Comparison\n( !==
).
const assert = require('assert');\n\nassert.notStrictEqual(1, 2);\n// OK\n\nassert.notStrictEqual(1, 1);\n// AssertionError: 1 !== 1\n\nassert.notStrictEqual(1, '1');\n// OK\n
\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 instead\nof 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
.
const assert = require('assert');\n\nassert.ok(true);\n// OK\nassert.ok(1);\n// OK\nassert.ok(false);\n// throws "AssertionError: false == true"\nassert.ok(0);\n// throws "AssertionError: 0 == true"\nassert.ok(false, 'it\\'s false');\n// throws "AssertionError: it's false"\n
\n"
},
{
"textRaw": "assert.strictEqual(actual, expected[, message])",
"type": "method",
"name": "strictEqual",
"meta": {
"added": [
"v0.1.21"
],
"changes": []
},
"signatures": [
{
"params": [
{
"textRaw": "`actual` {any} ",
"name": "actual",
"type": "any"
},
{
"textRaw": "`expected` {any} ",
"name": "expected",
"type": "any"
},
{
"textRaw": "`message` {any} ",
"name": "message",
"type": "any",
"optional": true
}
]
},
{
"params": [
{
"name": "actual"
},
{
"name": "expected"
},
{
"name": "message",
"optional": true
}
]
}
],
"desc": "Tests strict equality as determined by the Strict Equality Comparison\n( ===
).
const assert = require('assert');\n\nassert.strictEqual(1, 2);\n// AssertionError: 1 === 2\n\nassert.strictEqual(1, 1);\n// OK\n\nassert.strictEqual(1, '1');\n// AssertionError: 1 === '1'\n
\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 instead\nof the AssertionError
.
Expects the function block
to throw an error.
If specified, error
can be a constructor, RegExp
, or validation\nfunction.
If specified, message
will be the message provided by the AssertionError
if\nthe block fails to throw.
Validate instanceof using constructor:
\nassert.throws(\n () => {\n throw new Error('Wrong value');\n },\n Error\n);\n
\nValidate error message using RegExp
:
assert.throws(\n () => {\n throw new Error('Wrong value');\n },\n /value/\n);\n
\nCustom error validation:
\nassert.throws(\n () => {\n throw new Error('Wrong value');\n },\n function(err) {\n if ((err instanceof Error) && /value/.test(err)) {\n return true;\n }\n },\n 'unexpected error'\n);\n
\nNote that error
can not 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:
// THIS IS A MISTAKE! DO NOT DO THIS!\nassert.throws(myFunction, 'missing foo', 'did not throw with expected message');\n\n// Do this instead.\nassert.throws(myFunction, /missing foo/, 'did not throw with expected message');\n
\n"
}
],
"modules": [
{
"textRaw": "Caveats",
"name": "caveats",
"desc": "For the following cases, consider using ES2015 Object.is()
,\nwhich uses the SameValueZero comparison.
const a = 0;\nconst b = -a;\nassert.notStrictEqual(a, b);\n// AssertionError: 0 !== -0\n// Strict Equality Comparison doesn't distinguish between -0 and +0...\nassert(!Object.is(a, b));\n// but Object.is() does!\n\nconst str1 = 'foo';\nconst str2 = 'foo';\nassert.strictEqual(str1 / 1, str2 / 1);\n// AssertionError: NaN === NaN\n// Strict Equality Comparison can't be used to check NaN...\nassert(Object.is(str1 / 1, str2 / 1));\n// but Object.is() can!\n
\nFor more information, see\nMDN's guide on equality comparisons and sameness.
\n", "type": "module", "displayName": "Caveats" } ], "type": "module", "displayName": "Assert" } ] }