karma-jasmine-diff-reporter
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Karma reporter to highlight diffs of failed equality expectations for Jasmine.
Jasmine matchers that will be processed:
Example: 
Expectations have red background, actual results - green.
Note: there are matchers like toBeTruthy or toBeDefined in Jasmine, but they won't be highlighted because the messages outputed are Expected 0 to be truthy or Expected undefined to be defined respectively, and words truthy and defined are not the part of JavaScript. When using jasmine.objectContaining() message won't be highlighted too.
Note: if you use custom matchers, they also might be accidently highlighted, if their messages match the patterns I use to extract the data for comparison. There is no a solution to disable it yet. You can find more about custom matchers below.
Only Jasmine 2.x is supported, this extension will not work with Jasmine 1.3.
npm install karma-jasmine-diff-reporter --save-dev
Note: you also need to have karma and karma-jasmine installed
The idea behind karma-jasmine-diff-reporter is that it does not output info by itself, but just modifies the message, so as a result you can use it in conjunction with your favorite reporter. To do so, you have to put it before reporter you normally use in the Karma config file:
// karma.conf.js
module.exports = function(config) {
config.set({
frameworks: ['jasmine'],
// use Progress reporter and still highlight diffs
reporters: ['jasmine-diff', 'progress']
// reporters: ['jasmine-diff, 'mocha'] // karma-mocha-reporter
// reporters: ['jasmine-diff', 'nested'] // karma-nested-reporter
// reporters: ['jasmine-diff'] // use Karma default Base reporter
});
};
Otherwise, if you do not use any extra reporters, Karma Base reporter will be used by default.
Because of this specific order-dependent behavior some of the reporters that are listed after jasmine-diff might break (for example karma-junit-reporter which converts result into XML, which does not support characters used to set colors in terminal).
reporters: ['jasmine-diff', 'junit']
The workaround is actually to put jasmine-diff after broken reporter:
reporters: ['junit', 'jasmine-diff']
Karma config has an option colors which accepts a boolean value telling whether or not colors should be used in output. If this option is set to false, then karma-jasmine-diff-reporter will print diffs using inverse colors.
// karma.conf.js
module.exports = function(config) {
config.set({
frameworks: ['jasmine'],
reporters: ['jasmine-diff'],
colors: false
});
};
Example: 
Also you can explicitly specify what colors you want to see for diffs:
// karma.conf.js
module.exports = function(config) {
config.set({
frameworks: ['jasmine'],
reporters: ['jasmine-diff'],
jasmineDiffReporter: {
// Bg - background
// Fg - foreground (text)
color: {
expectedBg: 'bgYellow', // default 'bgRed'
expectedFg: 'black', // default 'white'
actualBg: 'bgCyan', // default 'bgGreen'
actualFg: 'red', // default 'white',
defaultBg: 'white', // default - none
defaultFg: 'grey' // default - none,
expectedWhitespaceBg: 'bgYellow', // default 'bgRed'
actualWhitespaceBg: 'bgCyan' // default 'bgGreen'
}
}
});
};
Example: 
You can use any colors that a supported by chalk.
defaultBg and defaultFg - for parts of the diff that were not changed, it allows to highlight the rest of the object and distinguish it from matcher textexpectedWhitespaceBg and actualWhitespaceBg - for the cases when you have a diff background of the same color as a terminal and only foreground color is used to identify diffs. In this case whitespace diffs won't be visible, when diff background has the same color as a terminal. To workaround it, it is possible to set a separate background for whitespace only using these options.To use default terminal color use empty value:
// karma.conf.js
module.exports = function(config) {
config.set({
jasmineDiffReporter: {
color: {
expectedBg: '', // default 'bgRed'
expectedFg: 'green', // default 'white'
actualBg: '', // default 'bgGreen'
actualFg: 'red', // default 'white',
}
}
});
};
If you have colors:false in Karma config, none of the custom or default colors will be used, diffs will be inversed instead.
If you have custom Jasmine matchers, which compare your data for equality, but the message of your matchers does not fit to karma-jasmine-diff-reporter, you can specify the rules to extract the objects for comparison of the custom matcher in the configuration:
// karma.conf.js
module.exports = function(config) {
config.set({
frameworks: ['jasmine'],
reporters: ['jasmine-diff']
jasmineDiffReporter: {
matchers: {
toLookTheSameAs: {
pattern: /Expected ([\S\s]*?) to look the same as ([\S\s]*?)\./,
reverse: true
}
}
}
});
};
Matcher must have a property called pattern, which is a pattern to parse a failure message. It should have two capturing groups, which will capture your data to compare. If you have less or more - it will be ignored. Suggested regular expression for capturing group is [\S\s]*, which will capture all characters including whitespaces in non-greedy way. Also there is an optional property reverse, if it is set to true, then the colors, which are used to highlight actual and expected data objects, should be switched. By default, first capturing group stands for expected data and second - for actual data. You can take a look at the definitions of default matchers here in the source code. You can even override default matchers by using their property name in config file (do it at your own risk).
Note: this feature is experimental and may cover just a few cases and may not cover a lot more, because custom matchers can be way to custom. But if there are some stable libraries, which provide popular custom matchers (like Jasmine-Matchers) and you think you want it to be supported, let me know the use-cases in the issues.
Pretty print option enables output of each key/value pair for an object and/or array on a new line, each line indentation depends on nesting level. Option is disabled by default. Set pretty option to true to enable default indentation - 2 spaces. You can also pass a string or a number instead of true. String will represent one level on indentation, number - number of spaces for one level of indentation. It is also possible to override pretty option for particular matchers, it will be used in favor of global option, so you could customize or even disable pretty output for any matchers (built-in or custom).
// karma.conf.js
module.exports = function(config) {
config.set({
frameworks: ['jasmine'],
reporters: ['jasmine-diff']
jasmineDiffReporter: {
pretty: true, // 2 spaces by default for one indent level
// pretty: ' ' // string - string to be used for one indent level
// pretty: 4 // number - number of spaces for one indent level
matchers: {
toEqual: {
pretty: false // disable pretty print for toEqual
},
toHaveBeenCalledWith: {
pretty: '___' // use 3 underscores for one indent level
}
}
}
});
};
Example: 
Multiline option provides extra formatting by adding newlines before and after diffed objects so they can spotted even easier. Setting multiline to true will add 2 newlines before and 2 after for both actual and expected object, and will also indent them by 2 spaces. It can also be configured individually - for each sub-option before, after and indent you can pass a string or a number. String will be used once per options as is, number - number of newlines (for before and after) or number of spaces (for indent). It is also possible to override multiline option for particular matchers, it will be used in favor of global option, so you could customize or even disable multiline output for any matchers (built-in or custom). It works really good along with pretty option turned on (see pretty).
// karma.conf.js
module.exports = function(config) {
config.set({
frameworks: ['jasmine'],
reporters: ['jasmine-diff']
jasmineDiffReporter: {
multiline: true, // before: 2 newlines, after: 2 newlines, indent: 2 spaces
matchers: {
toEqual: {
multiline: false // disable multiline for toEqual
}
}
}
});
};
Example: 
Configure individually:
// karma.conf.js
module.exports = function(config) {
config.set({
frameworks: ['jasmine'],
reporters: ['jasmine-diff']
jasmineDiffReporter: {
multiline: {
before: 1, // 1 newline
after: 3, // 3 newlines
indent: 4 // 4 spaces
// indent: '\t' // 1 tab
// indent: ' ' // 4 spaces
}
matchers: {
toHaveBeenCalledWith: {
multiline: {
before: 1 // use 1 newline before objects
}
}
}
}
});
};
JSON option allows to have output to be formatted as JSON instead of using Jasmine default pretty-printer, which adds extras like Object({}), so it could be possible to copy JSON right from terminal and use it. Setting json option to true will turn the feature on for all supported matchers, instead of toThrow and toThrowError, because there is no way to correctly represent errors in JSON format. The option can't be configured individually for each matcher, it will affect all of them. Internally objects are passed to JSON.stringify.
// karma.conf.js
module.exports = function(config) {
config.set({
frameworks: ['jasmine'],
reporters: ['jasmine-diff']
jasmineDiffReporter: {
json: true // format results as JSON
}
});
};
Diffs won't be displayed for a deep nested objects or large arrays, a threshold for these situations is configured in Jasmine. By default it has object nest level MAX_PRETTY_PRINT_DEPTH = 40 and array length MAX_PRETTY_PRINT_ARRAY_LENGTH = 100. It means that if the diff is out of these bounds, then Jasmine will return the same strings for both compared objects and karma-jasmine-diff-reporter won't be able to highlight those diffs.
FAQs
Diff and pretty print for failed tests
We found that karma-jasmine-diff-reporter 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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