power-assert
Advanced tools
The power-assert npm package is a powerful assertion library for JavaScript. It enhances the standard assertion functionality by providing more descriptive and readable assertion messages, which makes debugging easier. It is particularly useful for testing and development, as it helps developers quickly identify the root cause of test failures.
Basic Assertion
This feature allows you to perform basic assertions. If the assertion fails, power-assert provides a detailed message showing the values of the variables involved in the assertion.
const assert = require('power-assert');
const a = 1;
const b = 2;
assert(a === b);Complex Expression Assertion
Power-assert can handle complex expressions and provide detailed messages that break down the expression into its components, making it easier to understand why an assertion failed.
const assert = require('power-assert');
const user = { name: 'John', age: 30 };
assert(user.age > 20 && user.name === 'Doe');Custom Message
You can provide custom messages for assertions. If the assertion fails, the custom message is displayed along with the detailed breakdown of the assertion.
const assert = require('power-assert');
const x = 5;
const y = 10;
assert(x > y, 'x should be greater than y');Chai is a BDD / TDD assertion library for node and the browser that can be delightfully paired with any JavaScript testing framework. It provides a variety of assertion styles (should, expect, assert) and is highly extensible. Compared to power-assert, Chai offers more flexibility in terms of assertion styles but does not provide the same level of detailed assertion messages.
Jest is a delightful JavaScript Testing Framework with a focus on simplicity. It works out of the box with minimal configuration and provides a rich API for assertions. Jest's built-in assertion library is less detailed in its failure messages compared to power-assert, but it integrates seamlessly with the Jest testing framework and offers a wide range of features for testing.
The assert module provides a simple set of assertion tests that can be used to test invariants. It is part of Node.js core and is very basic compared to power-assert. While it is straightforward and easy to use, it lacks the detailed and descriptive assertion messages that power-assert provides.
Power Assert in JavaScript. Less code, more information.
power-assert is an implementation of "Power Assert" concept in JavaScript.
power-assert family is composed of four modules.
| module | description |
|---|---|
| power-assert | assert function wrapper on top of empower module. |
| empower | Power Assert feature enhancer for assert function/object. |
| espower | Power Assert feature instrumentor based on the Mozilla JavaScript AST. |
| grunt-espower | A grunt task to apply espower to target files. |
power-assert provides standard assert compatible function with Power Assert feature. (Best fit with Mocha. If you use assert-like objects provided by various testing frameworks such as QUnit or nodeunit. Please use empower module directly).
Internally, power-assert uses empower module to enhance power assert feature into the standard assert module, to run with the power assert feature added code by espower module.
See power-assert-demo project for power-assert Demo running with mocha (includes power-assert demo running with CoffeeScriptRedux ).
Please note that power-assert is a beta version product. Pull-requests, issue reports and patches are always welcomed.
var assert = require('power-assert');
describe('Array', function(){
beforeEach(function(){
this.ary = [1,2,3];
});
describe('#indexOf()', function(){
it('should return index when the value is present', function(){
var zero = 0, two = 2;
assert(this.ary.indexOf(zero) === two);
});
it('should return -1 when the value is not present', function(){
var minusOne = -1, two = 2;
assert.ok(this.ary.indexOf(two) === minusOne, 'THIS IS AN ASSERTION MESSAGE');
});
});
});
grunt-espower task to code above then run tests. See the power-assert output appears. $ mocha /path/to/espowered_examples/mocha_node.js
Array
#indexOf()
1) should return index when the value is present
2) should return -1 when the value is not present
0 passing (7 ms)
2 failing
1) Array #indexOf() should return index when the value is present:
AssertionError: # /path/to/examples/mocha_node.js:10
assert(this.ary.indexOf(zero) === two);
| | | | |
| | | | 2
| -1 0 false
[1,2,3]
at Object.empoweredAssert [as ok] (/path/to/node_modules/empower/lib/empower.js:97:25)
at powerAssert (/path/to/node_modules/empower/lib/empower.js:131:25)
at Context.<anonymous> (/path/to/examples/mocha_node_espowered.js:13:13)
at Test.Runnable.run (/path/to/node_modules/mocha/lib/runnable.js:211:32)
at Runner.runTest (/path/to/node_modules/mocha/lib/runner.js:355:10)
at /path/to/node_modules/mocha/lib/runner.js:401:12
at next (/path/to/node_modules/mocha/lib/runner.js:281:14)
at /path/to/node_modules/mocha/lib/runner.js:290:7
at next (/path/to/node_modules/mocha/lib/runner.js:234:23)
at Object._onImmediate (/path/to/node_modules/mocha/lib/runner.js:258:5)
at processImmediate [as _immediateCallback] (timers.js:330:15)
2) Array #indexOf() should return -1 when the value is not present:
AssertionError: THIS IS AN ASSERTION MESSAGE # /path/to/examples/mocha_node.js:14
assert.ok(this.ary.indexOf(two) === minusOne, 'THIS IS AN ASSERTION MESSAGE');
| | | | |
| | | | -1
| 1 2 false
[1,2,3]
at Function.empoweredAssert [as ok] (/path/to/node_modules/empower/lib/empower.js:97:25)
at Context.<anonymous> (/path/to/examples/mocha_node_espowered.js:48:20)
at Test.Runnable.run (/path/to/node_modules/mocha/lib/runnable.js:211:32)
at Runner.runTest (/path/to/node_modules/mocha/lib/runner.js:355:10)
at /path/to/node_modules/mocha/lib/runner.js:401:12
at next (/path/to/node_modules/mocha/lib/runner.js:281:14)
at /path/to/node_modules/mocha/lib/runner.js:290:7
at next (/path/to/node_modules/mocha/lib/runner.js:234:23)
at Object._onImmediate (/path/to/node_modules/mocha/lib/runner.js:258:5)
at processImmediate [as _immediateCallback] (timers.js:330:15)
First, declare power-assert and grunt-espower as devDependencies in your package.json, then run npm install.
(If you do not like Grunt, espower runner and its variation for Windows may be useful to start with.)
{
. . .
"devDependencies": {
"power-assert": "~0.2.0",
"grunt-espower": "~0.2.0",
. . .
},
. . .
}
Second, configure grunt-espower task to generate espowered code.
grunt.initConfig({
. . .
espower: {
test: {
files: [
{
expand: true, // Enable dynamic expansion.
cwd: 'test/', // Src matches are relative to this path.
src: ['**/*.js'], // Actual pattern(s) to match.
dest: 'espowered/', // Destination path prefix.
ext: '.js' // Dest filepaths will have this extension.
}
]
},
},
. . .
})
Third, generate espowered code using espower task.
$ grunt espower:test
Then run your test in your way. For example,
$ grunt test
or
$ mocha your_test_espowered.js
Licensed under the MIT license.
var q = require('qunitjs');
(function () {
var empower = require('empower'),
qunitTap = require("qunit-tap");
empower(q.assert, {destructive: true});
qunitTap(q, require('util').puts, {showSourceOnFailure: false});
q.init();
q.config.updateRate = 0;
})();
q.test('spike', function (assert) {
assert.ok(true);
var hoge = 'foo';
var fuga = 'bar';
assert.ok(hoge === fuga, 'comment');
var piyo = 3;
assert.ok(fuga === piyo);
var longString = 'very very loooooooooooooooooooooooooooooooooooooooooooooooooooong message';
var anotherLongString = 'yet another loooooooooooooooooooooooooooooooooooooooooooooooooooong message';
assert.ok(longString === anotherLongString);
assert.ok(4 === piyo);
assert.ok(4 !== 4);
var falsyStr = '';
assert.ok(falsyStr);
var falsyNum = 0;
assert.ok(falsyNum);
var ary1 = ['foo', 'bar'];
var ary2 = ['aaa', 'bbb', 'ccc'];
assert.ok(ary1.length === ary2.length);
assert.deepEqual(ary1, ary2);
var actual = 16;
assert.ok(5 < actual && actual < 13);
actual = 4;
assert.ok(5 < actual && actual < 13);
actual = 10;
assert.ok(actual < 5 || 13 < actual);
var propName = 'bar',
foo = {
bar: {
baz: false
}
};
assert.ok(foo.bar.baz);
assert.ok(foo['bar'].baz);
assert.ok(foo[propName]['baz']);
var truth = true;
assert.ok(!truth);
var func = function () { return false; };
assert.ok(func());
var obj = {
age: function () {
return 0;
}
};
assert.ok(obj.age());
var isFalsy = function (arg) {
return !(arg);
};
var positiveInt = 50;
assert.ok(isFalsy(positiveInt));
var sum = function () {
var result = 0;
for (var i = 0; i < arguments.length; i += 1) {
result += arguments[i];
}
return result;
};
var one = 1, two = 2, three = 3, seven = 7, ten = 10;
assert.ok(sum(one, two, three) === seven);
assert.ok(sum(sum(one, two), three) === sum(sum(two, three), seven));
assert.ok((three * (seven * ten)) === three);
var math = {
calc: {
sum: function () {
var result = 0;
for (var i = 0; i < arguments.length; i += 1) {
result += arguments[i];
}
return result;
}
}
};
assert.ok(math.calc.sum(one, two, three) === seven);
});
espower code above then running under Node.js# test: spike
ok 1
not ok 2 - comment # /path/to/examples/qunit_node.js:17
#
# assert.ok(hoge === fuga, 'comment');
# | | |
# | | "bar"
# | false
# "foo"
# , test: spike
not ok 3 - # /path/to/examples/qunit_node.js:20
#
# assert.ok(fuga === piyo);
# | | |
# | | 3
# | false
# "bar"
# , test: spike
not ok 4 - # /path/to/examples/qunit_node.js:24
#
# assert.ok(longString === anotherLongString);
# | | |
# | | "yet another loooooooooooooooooooooooooooooooooooooooooooooooooooong message"
# | false
# "very very loooooooooooooooooooooooooooooooooooooooooooooooooooong message"
# , test: spike
not ok 5 - # /path/to/examples/qunit_node.js:26
#
# assert.ok(4 === piyo);
# | |
# | 3
# false
# , test: spike
not ok 6 - # /path/to/examples/qunit_node.js:28
#
# assert.ok(4 !== 4);
# |
# false
# , test: spike
not ok 7 - # /path/to/examples/qunit_node.js:31
#
# assert.ok(falsyStr);
# |
# ""
# , test: spike
not ok 8 - # /path/to/examples/qunit_node.js:34
#
# assert.ok(falsyNum);
# |
# 0
# , test: spike
not ok 9 - # /path/to/examples/qunit_node.js:38
#
# assert.ok(ary1.length === ary2.length);
# | | | | |
# | | | | 3
# | | | ["aaa","bbb","ccc"]
# | 2 false
# ["foo","bar"]
# , test: spike
not ok 10 - # /path/to/examples/qunit_node.js:39
#
# assert.deepEqual(ary1, ary2);
# | |
# | ["aaa","bbb","ccc"]
# ["foo","bar"]
# , expected: [
# "aaa",
# "bbb",
# "ccc"
# ], got: [
# "foo",
# "bar"
# ], test: spike
not ok 11 - # /path/to/examples/qunit_node.js:42
#
# assert.ok(5 < actual && actual < 13);
# | | | | |
# | | | 16 false
# | 16 false
# true
# , test: spike
not ok 12 - # /path/to/examples/qunit_node.js:45
#
# assert.ok(5 < actual && actual < 13);
# | | |
# | 4 false
# false
# , test: spike
not ok 13 - # /path/to/examples/qunit_node.js:48
#
# assert.ok(actual < 5 || 13 < actual);
# | | | | |
# | | | | 10
# | | false false
# 10 false
# , test: spike
not ok 14 - # /path/to/examples/qunit_node.js:58
#
# assert.ok(foo.bar.baz);
# | | |
# | | false
# | {"baz":false}
# {"bar":{"baz":false}}
# , test: spike
not ok 15 - # /path/to/examples/qunit_node.js:59
#
# assert.ok(foo['bar'].baz);
# | | |
# | | false
# | {"baz":false}
# {"bar":{"baz":false}}
# , test: spike
not ok 16 - # /path/to/examples/qunit_node.js:60
#
# assert.ok(foo[propName]['baz']);
# | || |
# | |"bar" false
# | {"baz":false}
# {"bar":{"baz":false}}
# , test: spike
not ok 17 - # /path/to/examples/qunit_node.js:64
#
# assert.ok(!truth);
# ||
# |true
# false
# , test: spike
not ok 18 - # /path/to/examples/qunit_node.js:68
#
# assert.ok(func());
# |
# false
# , test: spike
not ok 19 - # /path/to/examples/qunit_node.js:76
#
# assert.ok(obj.age());
# | |
# {} 0
# , test: spike
not ok 20 - # /path/to/examples/qunit_node.js:83
#
# assert.ok(isFalsy(positiveInt));
# | |
# false 50
# , test: spike
not ok 21 - # /path/to/examples/qunit_node.js:94
#
# assert.ok(sum(one, two, three) === seven);
# | | | | | |
# | | | | | 7
# 6 1 2 3 false
# , test: spike
not ok 22 - # /path/to/examples/qunit_node.js:95
#
# assert.ok(sum(sum(one, two), three) === sum(sum(two, three), seven));
# | | | | | | | | | | |
# | | | | | | 12 5 2 3 7
# 6 3 1 2 3 false
# , test: spike
not ok 23 - # /path/to/examples/qunit_node.js:96
#
# assert.ok((three * (seven * ten)) === three);
# | | | | | | |
# | | | | | | 3
# | | | | 10 false
# | | 7 70
# 3 210
# , test: spike
not ok 24 - # /path/to/examples/qunit_node.js:110
#
# assert.ok(math.calc.sum(one, two, three) === seven);
# | | | | | | | |
# | | | | | | | 7
# | {} 6 1 2 3 false
# {"calc":{}}
# , test: spike
1..24
Have fun!
FAQs
Power Assert in JavaScript
The npm package power-assert receives a total of 74,313 weekly downloads. As such, power-assert popularity was classified as popular.
We found that power-assert demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 1 open source maintainer collaborating on the project.
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