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Power Assert in JavaScript. Provides descriptive assertion messages through standard assert interface. No API is the best API.
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README.md

power-assert

Power Assert in JavaScript. Provides descriptive assertion messages through standard assert interface. No API is the best API.

Build Status NPM package Bower package Dependency Status License

DESCRIPTION

What is power-assert?

power-assert provides descriptive assertion messages for your tests, like this.

  1) Array #indexOf() should return index when the value is present:
     AssertionError: # path/to/test/mocha_node.js:10

  assert(this.ary.indexOf(zero) === two)
              |   |       |     |   |
              |   |       |     |   2
              |   -1      0     false
              [1,2,3]

  [number] two
  => 2
  [number] this.ary.indexOf(zero)
  => -1

INSTALL

npm install --save-dev power-assert <one of instrumentors>

or

bower install --save-dev power-assert
npm install --save-dev <one of instrumentors>

see list of instrumentors

API

power-assert enhances these assert functions by espower. Produces descriptive message when assertion is failed.

  • assert(value, [message])
  • assert.ok(value, [message])
  • assert.equal(actual, expected, [message])
  • assert.notEqual(actual, expected, [message])
  • assert.strictEqual(actual, expected, [message])
  • assert.notStrictEqual(actual, expected, [message])
  • assert.deepEqual(actual, expected, [message])
  • assert.notDeepEqual(actual, expected, [message])
  • assert.deepStrictEqual(actual, expected, [message]) (io.js v1.2.0~)
  • assert.notDeepStrictEqual(actual, expected, [message]) (io.js v1.2.0~)

power-assert is fully compatible with assert. So functions below are also available though they are not enhanced (does not produce descriptive message).

  • assert.fail(actual, expected, message, operator)
  • assert.throws(block, [error], [message])
  • assert.doesNotThrow(block, [message])
  • assert.ifError(value)

power-assert provides an API for customization.

  • assert.customize(options)

No API is the best API

Though power-assert is fully compatible with standard assert interface, all you need to remember is just an assert(any_expression) function in most cases.

The core value of power-assert is absolute simplicity and stability. Especially, power-assert sticks to the simplest form of testing, assert(any_expression).

    assert(this.types[index].name === bob.name)
                |    ||      |    |   |   |
                |    ||      |    |   |   "bob"
                |    ||      |    |   Person{name:"bob",age:5}
                |    ||      |    false
                |    |11     "alice"
                |    Person{name:"alice",age:3}
                ["string",98.6,true,false,null,undefined,#Array#,#Object#,NaN,Infinity,/^not/,#Person#]

    --- [string] bob.name
    +++ [string] this.types[index].name
    @@ -1,3 +1,5 @@
    -bob
    +alice

CHANGELOG

See CHANGELOG

FAQ

EXAMPLE

See HOW TO USE section for more details.

Note: There is an online demo site available.

Target test code (using Mocha in this example)

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');
        });
    });
});

describe('various types', function(){
    function Person(name, age) {
        this.name = name;
        this.age = age;
    }
    beforeEach(function(){
        this.types = [
            'string', 98.6, true, false, null, undefined,
            ['nested', 'array'],
            {object: true},
            NaN, Infinity,
            /^not/,
            new Person('alice', 3)
        ];
    });
    it('demo', function(){
        var index = this.types.length -1,
            bob = new Person('bob', 5);
        assert(this.types[index].name === bob.name);
    });
});

Be sure to transform test code

To use power-assert, you need to transform your test code for power-assert output.

Code transform is done by instrumentors below:

If you are using Node.js only, the easiest way is to use intelli-espower-loader. Steps are as follows.

Setup

npm install --save-dev mocha power-assert intelli-espower-loader

Run

Put tests into test directory then run. You will see the power-assert output appears.

  $ $(npm bin)/mocha --require intelli-espower-loader path/to/test/mocha_node.js


  Array
    #indexOf()
      1) should return index when the value is present
      2) should return -1 when the value is not present

  various types
    3) demo


  0 passing (43ms)
  3 failing

  1) Array #indexOf() should return index when the value is present:

      AssertionError:   # test/mocha_node.js:10

  assert(this.ary.indexOf(zero) === two)
              |   |       |     |   |
              |   |       |     |   2
              |   -1      0     false
              [1,2,3]

  [number] two
  => 2
  [number] this.ary.indexOf(zero)
  => -1

      + expected - actual

      -false
      +true

      at Context.<anonymous> (test/mocha_node.js:10:13)

  2) Array #indexOf() should return -1 when the value is not present:

      AssertionError: THIS IS AN ASSERTION MESSAGE   # test/mocha_node.js:14

  assert.ok(this.ary.indexOf(two) === minusOne, 'THIS IS AN ASSERTION MESSAGE')
                 |   |       |    |   |
                 |   |       |    |   -1
                 |   1       2    false
                 [1,2,3]

  [number] minusOne
  => -1
  [number] this.ary.indexOf(two)
  => 1

      + expected - actual

      -false
      +true

      at Context.<anonymous> (test/mocha_node.js:14:20)

  3) various types demo:

      AssertionError:   # test/mocha_node.js:37

  assert(this.types[index].name === bob.name)
              |    ||      |    |   |   |
              |    ||      |    |   |   "bob"
              |    ||      |    |   Person{name:"bob",age:5}
              |    ||      |    false
              |    |11     "alice"
              |    Person{name:"alice",age:3}
              ["string",98.6,true,false,null,undefined,#Array#,#Object#,NaN,Infinity,/^not/,#Person#]

  --- [string] bob.name
  +++ [string] this.types[index].name
  @@ -1,3 +1,5 @@
  -bob
  +alice


      + expected - actual

      -false
      +true

      at Context.<anonymous> (test/mocha_node.js:37:9)

SEED PROJECTS

Some seed projects are available to help you start with power-assert.

module env tech stack
power-assert-node-seed Node.js power-assert + intelli-espower-loader
power-assert-testem-seed Browsers(by testem) power-assert + gulp-espower + testem.
power-assert-karma-seed Browsers(by Karma) power-assert + espowerify + browserify + Karma.

HOW TO USE

There are four ways to use power-assert. (If you want to see running examples, see SEED PROJECTS)

  1. power-assert + espower-loader: Highly recommended but only works under Node.
  2. power-assert + Babel + babel-plugin-espower: Recommended if you are writing ES6 with Babel or babelify with browserify
  3. power-assert + espower-coffee or espower-typescript or espower-traceur or espower-babel : Use power-assert through transpilers. Recommended but only works under Node.
  4. power-assert + espowerify or webpack-espower-loader: Recommended if you are using browserify or webpack.
  5. power-assert + espower-cli or grunt-espower or gulp-espower : Generate instrumented code so works anywhere.

using espower-loader

If you are writing Node.js app/module, you can instrument Power Assert feature without code generation by using espower-loader.

First, install power-assert and espower-loader via npm.

$ npm install --save-dev power-assert espower-loader

Second, require power-assert in your test.

--- a/test/your_test.js
+++ b/test/your_test.js
@@ -1,4 +1,4 @@
-var assert = require('assert');
+var assert = require('power-assert');

Third, put enable-power-assert.js somewhere in your project, where pattern matches to target test files.

require('espower-loader')({
    // directory where match starts with
    cwd: process.cwd(),
    // glob pattern using minimatch module
    pattern: 'test/**/*.js'
});

Then run mocha, with --require option. No code generation required.

$ $(npm bin)/mocha --require ./path/to/enable-power-assert test/your_test.js

FYI: You may be interested in intelli-espower-loader to go one step further. With intelli-espower-loader, you don't need to create loader file (like enable-power-assert.js). Just define test directory in package.json wow!

using espower-coffee

If you are writing Node.js app/module in CoffeeScript, you can instrument Power Assert feature without code generation by using espower-coffee.

see espower-coffee README.

using espower-typescript

If you are writing Node.js app/module in TypeScript, you can instrument Power Assert feature without code generation by using espower-typescript.

see espower-typescript README.

using babel-plugin-espower

If you are writing your code in ES6, you can instrument Power Assert feature with Babel and babel-plugin-espower.

see babel-plugin-espower README.

using espower-traceur or espower-babel

If you are writing Node.js app/module in ES6, you can instrument Power Assert feature without code generation by using espower-traceur or espower-babel. espower-traceur uses Traceur Compiler, espower-babel uses Babel.

see espower-traceur README or espower-babel README.

using espowerify

On the browser side and you are using browserify, you can instrument Power Assert feature via espowerify.

see espowerify README.

using webpack-espower-loader

If you are using webpack, you can instrument Power Assert feature via webpack-espower-loader.

see webpack-espower-loader README.

using espower-cli

On the browser side and you don't want to use grunt,gulp or browserify, you can use power-assert via bower, with generated code by espower-cli

First, install power-assert via bower and espower-cli via npm. This means that you run espower command (on Node), then run tests on browser.

$ bower install --save-dev power-assert
$ npm install --save-dev espower-cli

Second, require build/power-assert.js (all-in-one build for browsers) in your test html.

<script type="text/javascript" src="./path/to/bower_components/power-assert/build/power-assert.js"></script>

Then, generate espowered code.

$ espower test/your_test.js > powered/your_test.js

Lastly, run your test in your way. For example,

$ mocha-phantomjs path/to/test.html

using grunt-espower

On the browser side and you are not using browserify but bower and Grunt, you can use power-assert via bower, with generated code by grunt-espower

First, install power-assert via bower and grunt-espower via npm. This means that you run grunt (on Node), then run tests on browser.

$ bower install --save-dev power-assert
$ npm install --save-dev grunt-espower

Second, require build/power-assert.js (all-in-one build for browsers) in your test html.

<script type="text/javascript" src="./path/to/bower_components/power-assert/build/power-assert.js"></script>

Third, 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.
        }
      ]
    },
  },

  . . . 

})

Then, generate espowered code using espower task.

$ grunt espower:test

Lastly, run your test in your way. For example,

$ grunt test

using gulp-espower

On the browser side and you are not using browserify but bower and gulp, you can use power-assert via bower, with generated code by gulp-espower

First, install power-assert via bower and gulp-espower via npm. This means that you run gulp (on Node), then run tests on browser.

$ bower install --save-dev power-assert
$ npm install --save-dev gulp-espower

Second, require build/power-assert.js (all-in-one build for browsers) in your test html.

<script type="text/javascript" src="./path/to/bower_components/power-assert/build/power-assert.js"></script>

Third, configure gulp-espower task to generate espowered code.

var gulp = require('gulp'),
    espower = require('gulp-espower');
  . . . 
gulp.task('espower', function() {
    return gulp
        .src('test/**/*_test.js', {base: './test/'})
        .pipe(espower())
        .pipe(gulp.dest('espowered'));
});
  . . . 
})

Then, generate espowered code (in this example, using espower task).

$ gulp espower

Lastly, run your test in your way. For example,

$ gulp test

CUSTOMIZATION API

power-assert provides an API for customization.

var assert = assert.customize(options)

Through this API, you can customize power-assert by changing some options.

var assert = require('power-assert').customize({
    output: {
        maxDepth: 2
    }
});

options

options has two top-level keys. assertion and output.

options.assertion

customization options for empower module. See empower API documentation for details. Note that some default values are different from empower's (modifyMessageOnRethrow: true and saveContextOnRethrow: true).

options.output

customization options for power-assert-formatter module. See power-assert-formatter API documentation for details.

default values

customizable properties and their default values are as follows.

var assert = require('power-assert').customize({
    assertion: {
        destructive: false,
        modifyMessageOnRethrow: true,
        saveContextOnRethrow: true,
        patterns: [
            'assert(value, [message])',
            'assert.ok(value, [message])',
            'assert.equal(actual, expected, [message])',
            'assert.notEqual(actual, expected, [message])',
            'assert.strictEqual(actual, expected, [message])',
            'assert.notStrictEqual(actual, expected, [message])',
            'assert.deepEqual(actual, expected, [message])',
            'assert.notDeepEqual(actual, expected, [message])',
            'assert.deepStrictEqual(actual, expected, [message])',
            'assert.notDeepStrictEqual(actual, expected, [message])'
        ]
    },
    output: {
        lineDiffThreshold: 5,
        maxDepth: 1,
        anonymous: 'Object',
        circular: '#@Circular#',
        lineSeparator: '\n',
        ambiguousEastAsianCharWidth: 2,
        widthOf: (Function to calculate width of string. Please see power-assert-formatter's documentation)
        stringify: (Function to stringify any target value. Please see power-assert-formatter's documentation)
        diff: (Function to create diff string between two strings. Please see power-assert-formatter's documentation)
        writerClass: (Constructor Function for output writer class. Please see power-assert-formatter's documentation)
        renderers: [
            './built-in/file',
            './built-in/assertion',
            './built-in/diagram',
            './built-in/binary-expression'
        ]
    }
});

INTERNAL DESIGN

power-assert family provides 1 main module, 4 core modules and many more instrumentors.

Main (facade) module is,

module description
power-assert Standard assert function on top of empower and power-assert-formatter

core modules are,

module description
empower Power Assert feature enhancer for assert function/object.
power-assert-formatter Power Assert output formatter.
espower Power Assert feature instrumentor core based on the ECMAScript AST defined in The ESTree Spec (formerly known as Mozilla SpiderMonkey Parser API).
espower-source Power Assert instrumentor from source to source, with source-map. (Thin wrapper of espower).

and instrumentors are,

module description
espower-cli Command line tool for power-assert.
espower-loader Node module loader to apply espower on the fly.
intelli-espower-loader configure espower-loader with ease.
babel-plugin-espower Babel plugin to instrument power-assert feature into target files.
espowerify Browserify transform to apply espower to target files.
webpack-espower-loader Power Assert instrumentor module for webpack.
grunt-espower Grunt task to apply espower to target files.
gulp-espower Gulp plugin to apply espower to target files.
karma-espower-preprocessor karma-preprocessor for power-assert.
espower-coffee power-assert instrumentor for CoffeeScript.
espower-typescript power-assert instrumentor for TypeScript.
espower-traceur power-assert instrumentor for ES6 using Traceur Compiler.
espower-babel power-assert instrumentor for ES6 using Babel.

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 and power-assert-formatter modules 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, and prettify output using power-assert-formatter.

See power-assert-demo project for power-assert Demo running with mocha.

SUPPORTED FRAMEWORK

FRAMEWORKS KNOWN TO WORK

AUTHOR

CONTRIBUTORS

LICENSE

Licensed under the MIT license.

MORE OUTPUT EXAMPLES

Target test code (using QUnit in this example)

var q = require('qunitjs');

(function () {
    var empower = require('empower'),
        formatter = require('power-assert-formatter'),
        qunitTap = require("qunit-tap");
    empower(q.assert, formatter(), {destructive: true});
    qunitTap(q, require('util').puts, {showSourceOnFailure: false});
    q.config.autorun = false;
})();

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);
});

q.load();

espower code above then running under Node.js

# module: undefined
# test: spike
ok 1 - okay
not ok 2 - comment # path/to/examples/qunit_node.js:17
#
# assert.ok(hoge === fuga, 'comment')
#           |    |   |
#           |    |   "bar"
#           |    false
#           "foo"
#
# --- [string] fuga
# +++ [string] hoge
# @@ -1,3 +1,3 @@
# -bar
# +foo
#
# , test: spike
not ok 3 - # path/to/examples/qunit_node.js:20
#
# assert.ok(fuga === piyo)
#           |    |   |
#           |    |   3
#           |    false
#           "bar"
#
# [number] piyo
# => 3
# [string] fuga
# => "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"
#
# --- [string] anotherLongString
# +++ [string] longString
# @@ -1,15 +1,13 @@
# -yet anoth
# +very v
#  er
# +y
#   loo
#
# , test: spike
not ok 5 - # path/to/examples/qunit_node.js:26
#
# assert.ok(4 === piyo)
#             |   |
#             |   3
#             false
#
# [number] piyo
# => 3
# [number] 4
# => 4
# , 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"]
#
# [number] ary2.length
# => 3
# [number] ary1.length
# => 2
# , 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
#           |   Object{baz:false}
#           Object{bar:#Object#}
# , test: spike
not ok 15 - # path/to/examples/qunit_node.js:59
#
# assert.ok(foo['bar'].baz)
#           |  |       |
#           |  |       false
#           |  Object{baz:false}
#           Object{bar:#Object#}
# , test: spike
not ok 16 - # path/to/examples/qunit_node.js:60
#
# assert.ok(foo[propName]['baz'])
#           |  ||        |
#           |  |"bar"    false
#           |  Object{baz:false}
#           Object{bar:#Object#}
# , 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
#           Object{age:#function#}
# , 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
#
# [number] seven
# => 7
# [number] sum(one, two, three)
# => 6
# , 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
#
# [number] sum(sum(two, three), seven)
# => 12
# [number] sum(sum(one, two), three)
# => 6
# , 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
#
# [number] three
# => 3
# [number] three * (seven * ten)
# => 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
#           |    Object{sum:#function#}
#           Object{calc:#Object#}
#
# [number] seven
# => 7
# [number] math.calc.sum(one, two, three)
# => 6
# , test: spike
1..24

Have fun!

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