Failed commitments in Protractor/WebDriverJS

Question

Failed commitments in Protractor/WebDriverJS

WebdriverIO and Protractor are built on the concept of promises:

Both WebdriverIO (and as a result, Protractor) APIs operate asynchronously. All functions return promises. WebdriverIO maintains a queue of pending promises known as the control flow to ensure organized execution.

Referencing the definition:

A promise is an object that represents a value or the future computation of a value. Initially, every promise is in a pending state and can either be successfully resolved with a value or be rejected to signal an error.

The aspect regarding promise rejection is something that I haven't fully grasped yet and have not encountered in Protractor. Typically, we utilize the pattern of using then() and supplying a function for handling a successfully resolved promise:

element(by.css("#myid")).getAttribute("value").then(function (value) {
    // manipulate the value here
});

The Query:

Is there a possibility that a promise returned by any of the Protractor/WebDriverJS functions may not be successfully resolved and could potentially be rejected? Is it necessary to consider this scenario and address it?

javascript selenium testing promise protractor

Answer 1

Answer №1

During my usage of browser.wait(), I encountered a scenario involving promise rejection. Allow me to share an example:

var EC = protractor.ExpectedConditions;

function isElementVisible() {

    var el = element(by.css('#myel'));

    // return promise
    return browser.wait(EC.visibilityOf(el), 1000)
    .then(function success() {
        return true; // return if promise resolved
    }, function fail() {
        return false; // return if promise rejected
    });
}

expect(isElementVisible()).toBe(true);
expect(isElementVisible()).toBe(false);

In this case, the success function will be executed if the element is present on the page. Conversely, if the element is not found after 1 second, the fail function will handle the rejection. One key aspect to note is that by providing a callback for rejection, one can ensure consistency in expectations. By anticipating whether the promise will resolve to true or false, it becomes feasible to construct a suite based on this behavior. Failure to include a fail callback could result in an uncaught exception due to timeout, leading to the failure of a specific test while allowing others to proceed. Although Protractor intercepts such exceptions, handling them within the codebase is pivotal to prevent leaks.

Answer 2

During my usage of browser.wait(), I encountered a scenario involving promise rejection. Allow me to share an example:

var EC = protractor.ExpectedConditions;

function isElementVisible() {

    var el = element(by.css('#myel'));

    // return promise
    return browser.wait(EC.visibilityOf(el), 1000)
    .then(function success() {
        return true; // return if promise resolved
    }, function fail() {
        return false; // return if promise rejected
    });
}

expect(isElementVisible()).toBe(true);
expect(isElementVisible()).toBe(false);

In this case, the success function will be executed if the element is present on the page. Conversely, if the element is not found after 1 second, the fail function will handle the rejection. One key aspect to note is that by providing a callback for rejection, one can ensure consistency in expectations. By anticipating whether the promise will resolve to true or false, it becomes feasible to construct a suite based on this behavior. Failure to include a fail callback could result in an uncaught exception due to timeout, leading to the failure of a specific test while allowing others to proceed. Although Protractor intercepts such exceptions, handling them within the codebase is pivotal to prevent leaks.

Answer 3

Answer №2

One of the advantages of using promises is that you will always receive a response, whether it's data or an error message. This applies even when working with multiple promises in a series, such as those used in Webdriver - you will either get an array of responses or a failure response if one of them fails. How you choose to handle these failed responses is ultimately up to you; personally, I prefer to log them into the console for review. The key decision lies in whether you want to abort the rest of your tests or continue despite the errors.

If you're looking for more information on this topic, check out this informative article:

It seems like what you're currently doing is sufficient, but keep in mind that you're not actively catching any of the errors. If this is something you're concerned about, consider abstracting the call into a function that automatically handles and logs errors for you.

Answer 4

One of the advantages of using promises is that you will always receive a response, whether it's data or an error message. This applies even when working with multiple promises in a series, such as those used in Webdriver - you will either get an array of responses or a failure response if one of them fails. How you choose to handle these failed responses is ultimately up to you; personally, I prefer to log them into the console for review. The key decision lies in whether you want to abort the rest of your tests or continue despite the errors.

If you're looking for more information on this topic, check out this informative article:

It seems like what you're currently doing is sufficient, but keep in mind that you're not actively catching any of the errors. If this is something you're concerned about, consider abstracting the call into a function that automatically handles and logs errors for you.

Failed commitments in Protractor/WebDriverJS

Answer №1

Answer №2

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