Nanobot: Polygonal Mascot


1.0.0 • Public • Published


Carahue integrates Mocha, SpookyJS, and node-resemble for automated layout and render testing of web-based projects.

describe('checkout', function() {
  page('signin', 'signin', function() {
      .thenScreenshot('errors', '.info-header');

See example for complete examples.


Carahue extends the Mocha BDD API with the page and beforePage helpers. These may be used in conjuntion with normal Mocha BDD directives but the Carahue context is only available within these methods.

#page(name, route[, options, callback])

Defines a Carahue test.

  • name Name of the test
  • route Route/URL to execute the test. This is relative to routePrefix, if defined.
  • options Optional hash object with additional test options.
    • before Callback executed before the screenshot but after all beforePage instances
    • selector Selector to use when taking screenshot. Defaults to the entire page.
    • ignore Elements to ignore when taking screenshots. This value is applied in addition to globalIgnore
    • after Callback to execute after the initial screenshot.
  • callback Callback to execute after the initial screenshot. May be used to define additional tests. Superceeds options.after.

See Context for discussion of the APIs available in the callback.


Called before each page test. Allows for test setup after the page has loaded, but before any screenshots have been taken.

See Context for discussion of the APIs available in the callback.


All callbacks in page and beforePage methods are run in the Carahue context. By default the context includes

  • thenCheck(query, check) Applies/removes the checked attribute for elements matching query
  • thenWaitForImages() Pauses test execution until all images in the DOM have been loaded
  • thenScreenshot(name[, selector, ignore]) Takes a screenshot of the current page state
    • name Name of the screenshot. This will be used to generate the output file name.
    • selector Optional selector to limit the screenshot to
    • ignore Optional list of elements to remove from the screenshot

Additionally the following Spooky methods are exposed on the context:

  • then
  • thenClick
  • thenEvaluate
  • thenOpen
  • thenOpenAndEvaluate

Discussion of these methods and the call structures can be found in the Spooky documentation and the Casper documentation.

Extending Context

The execution context may be extended using the carahue.context.extend(object) method.

  thenViewScreenshot: function(name) {
    return this.thenScreenshot(name, '[data-layout-cid]');

Any fields exposed on the object parameter will be applied to future contexts.


Configuration may be set via the carahue.config.extend(object) method, which will augment the config with the passed object value.

  casper: {
    viewportSize: {
      width: platform === 'ipad' ? 1024 : 320,
      height: platform === 'ipad' ? 768 : 480

Supported configuration values are:

  • child : PhantomJS runtime options.

    Defaults to

      'ignore-ssl-errors': 'yes',
      'web-security': 'false'

Is augmented rather than replaced when passed to extend.

  • casper : Casper runtime options

    Defaults to

      'pageSettings': {
        'userAgent': env.USER_AGENT
      'logLevel': 'info',
      'verbose': true

Is augmented rather than replaced when passed to extend.

  • screencapturePath : Path containing comparison screenshots.

    Defaults to env.SCREENCAPTURE_PATH or cwd

  • failurePath : Path to output comparison images from failed tests to.

    Defaults to env.FAILURE_PATH or "failure"

  • routePrefix : Prefix to apply to non-qualified routes.

    Defaults to empty.

  • globalIgnore : Selector of elements that are always to be ignored when taking screenshots.

Troubleshooting / Best Practices


The image comparison is fairly intollerant of changes to the output, by design. Where possible data should be mocked with static test data to reduce the number of changes due to content. When this is not possible, sections of consistently changing data should be ignored in the screenshot output to prevent false positive test failures.

Screenshot Images

If using git for version control for the project it's advisable to not include screenshot images for the tests in a location outside of the immediate github repository as this can create a lot of overhead as the tests change over time. Projects such as git-media may help resolve this issue.


The Casper runtime by default generates a significant amount of logging but the majority of this is not output unless the log and verbosity levels are set appropriately:

  casper: {
    logLevel: 'debug',
    verbose: true

When set as above this will enable any casper specific logging instructions. console.log statemements run by the page itself will log regardless of the values set here.

Often times timeout or missing selector errors are seen due to unexpected state of the page when the test is run. This snippet may be used as a base to log the page's HTML struture if errors are seen.

beforePage(function() {
    .thenEvaluate(function() {
      console.log('This always logs ' + $('.foo').html());
    .then(function() {
      // This logs if casper flags are set

Phantom Wrappers

Spooky utilizes a stdio-based IPC layer that relies on the Casper instance having access to both stdout and stdin.

Occasionally packages will attempt to override the phantomjs executable on the path and not implement forwarding for both streams. When this occurs generally the carahue tests will all hang. If this behavior is seen then verify that the phantomjs process on the path is the cannonical binary.


Carahue's internal tests may be run via

  grunt test




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