Expect API


Nightwatch provides a fluent BDD-style interface for performing assertions on elements, defined on the expect namespace on the main Nightwatch instance. It is based on the Chai Expect assertion library and provides a greater level of flexibility, also adding new capabilities over the classic assert interface.

It uses a chain-able language to construct assertions given an element specified by a css/xpath selector. A simple example looks like the following:

describe('expect example', function() {
  it('sample test', function (browser) {
    // start with identifying the element
    // and then assert the element is present
    // or assert the element is visible

Language Chains

The following are provided as chainable getters to improve the readability of your assertions. They do not provide testing capabilities and the order is not important.

  • to
  • be
  • been
  • is
  • that
  • which
  • and
  • has
  • have
  • with
  • at
  • does
  • of


These methods will perform assertions on the specified target on the current element. The targets can be an attribute value, the element's inner text and a css property.

this.demoTest = function (browser) {
  browser.expect.element('#main').text.to.equal('The Night Watch');
  browser.expect.element('#main').text.to.contain('The Night Watch');


Same as equal / contain / match.

this.demoTest = function (browser) {
browser.expect.element('#main').text.to.startWith('The'); };


Negates any of assertions following in the chain.

this.demoTest = function (browser) {
  browser.expect.element('#main').text.to.not.equal('The Night Watch');
browser.expect.element('#main').text.to.not.contain('The Night Watch');
browser.expect.element('#main').to.have.css('display').which.does.not.equal('block'); };


These methods perform the same thing which is essentially retrying the assertion for the given amount of time (in milliseconds). before or after can be chained to any assertion and thus adding retry capability.

You can change the polling interval by defining a waitForConditionPollInterval property (in milliseconds) as a global property in your nightwatch.json or in your external globals file. Similarly, a default timeout can be specified as a global waitForConditionTimeout property (in milliseconds).

this.demoTest = function (browser) {
  browser.expect.element('#main').text.to.contain('The Night Watch').before(1000);
browser.expect.element('#main').text.to.not.contain('The Night Watch').after(500); };

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