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Nightwatch with Visual Regression testing
// assertions/compareScreenshot.js
var resemble = require('resemble'),
fs = require('fs');
exports.assertion = function(filename, expected) {
var screenshotPath = 'test/screenshots/',
baselinePath = screenshotPath + 'baseline/' + filename,
resultPath = screenshotPath + 'results/' + filename,
diffPath = screenshotPath + 'diffs/' + filename;
this.message = 'Unexpected compareScreenshot error.';
this.expected = expected || 0; // misMatchPercentage tolerance default 0%
this.command = function(callback) {
// create new baseline photo if none exists
if (!fs.existsSync(baselinePath)) {
console.log('WARNING: Baseline Photo does NOT exist.');
console.log('Creating Baseline Photo from Result: ' + baselinePath);
fs.writeFileSync(baselinePath, fs.readFileSync(resultPath));
}
resemble
.resemble(baselinePath)
.compareTo(resultPath)
.ignoreAntialiasing()
.onComplete(callback); // calls this.value with the result
return this;
};
this.value = function(result) {
var diff = new Buffer(result.getImageDataUrl().replace(/data:image\/png;base64,/,''), 'base64');
fs.writeFileSync(diffPath, diff);
return parseFloat(result.misMatchPercentage, 10); // value this.pass is called with
};
this.pass = function(value) {
var pass = value <= this.expected;
if (pass) {
this.message = 'Screenshots Matched for ' + filename +
' with a tolerance of ' + this.expected + '%.';
} else {
this.message = 'Screenshots Match Failed for ' + filename +
' with a tolerance of ' + this.expected + '%.\n' +
' Screenshots at:\n' +
' Baseline: ' + baselinePath + '\n' +
' Result: ' + resultPath + '\n' +
' Diff: ' + diffPath + '\n' +
' Open ' + diffPath + ' to see how the screenshot has changed.\n' +
' If the Result Screenshot is correct you can use it to update the Baseline Screenshot and re-run your test:\n' +
' cp ' + resultPath + ' ' + baselinePath;
}
return pass;
};
};
// commands/compareScreenshot.js
exports.command = function(filename, expected, callback) {
var self = this,
screenshotPath = 'test/screenshots/',
resultPath = screenshotPath + 'results/' + filename;
self.saveScreenshot(resultPath, function(response) {
self.assert.compareScreenshot(filename, expected, function(result) {
if (typeof callback === 'function') {
callback.call(self, result);
}
});
});
return this; // allows the command to be chained.
};
module.exports = {
'My Test': function(browser) {
browser
.url('http://www.google.com')
.compareScreenshot('compare-google-screenshot.png')
.end();
}
};
@nhufinney

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commented Dec 11, 2015

It's wonderful. Thank you so much Richard.

@kavimukh

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commented May 24, 2016

So I have question, I should copy assertions-compareScreenshot.js and commands-compareScreenshot.js to specific folder? if so where?

@eric314

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commented May 25, 2016

Thank you for putting this together. It serves as a great starting point for a larger design delta automation regression suite using Resemble and Nightwatch!

@tryenc

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commented Dec 1, 2017

This was super helpful! Thanks very much!

@gkemp94

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commented Jan 5, 2018

Thanks so much for this! This is a perfect baseline for what I need to accomplish!

@kontrollanten

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commented Jan 14, 2018

Thanks for sharing! I've created a PR to nighwatchjs to make it possible to add the screenshots to the report.

@JoshuaMorris

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commented Jan 18, 2018

Any suggestions on how best to mask portions of the page you don't want to be included in the page capture and compare?

@markyvon2k

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commented Jan 24, 2018

@JoshuaMorris I've used nightwatch's .execute() to programmatically set elements' visibility to hidden to maintain page layout while masking dynamic content (dates/usernames etc) that shouldn't be included in capture and compare.

@AnishaAnchit

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commented May 7, 2019

I Used the code for nightwatch-cucumber framework . It worked except that if the images do not match, the message is received correctly but the test case is still marked as passed. how can we fix this? Also has anyone tried visual regression in browserstack? Any pointers would be appreciated.

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