The Main Algorithm

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The Main Algorithm

Selenide Advent Calendar
Day 1

Good December!

The Advent has begun.

Children are unpacking their advent calendars, opening one small window with a chocolate every day. In Java world, we have a Java Advent Calendar, in which many authors write a new article every day. I also participated in it could of times (2017 and 2018).

I also decided to start Selenide Advent Calendar. Every new day a new post. From 1st to 25th December. I am starting, and you can continue - just give me a notice by any possible way.

Today topic is:

The Main Algorithm

The main feature of Selenide, as many of you say, is automated waiting.
You don’t need to copy-paste boilerplate code like new WebDriverWait(driver, 30).until(ExpectedConditions.visibilityOfElementLocated(By.xpath("//div[contains(text(),'COMPOSE')]"))) to wait for some event. You don’t need to waste your time and effort to decide where a waiting is needed. You don’t need to see a flaky tests and investigate where you should add one more new WebDriverWait.

With Selenide, everything is much more simple. Any line like $(byText("COMPOSE")).shouldBe(visible) waits automatically if needed.

Doesn’t it slower my tests?

No.

If the element is already visible, Selenide will just go on. If not - Selenide will wait for 100 ms and check again. If still not, wait for another 100 ms and check again. So it will continue up to 4 seconds. And only if the element will not appear after 4 seconds, then Selenide will fail the test.

Of course, those numbers 4s and 100ms are configurable.

How it works?

We are getting to the Main Algorithm. Actually, it’s very simple.

For example, this is how $(".btn").shouldBe(visible) works:

void shouldBeVisible() {
  do {
    try {
      assert webdriver.findElement().isDisplayed() == true;
      return ok;
    }
    catch (Exception e) {
      sleep(100 мс)
    }
  } while (less than N seconds);
  throw new ElementShouldBeVisible("Expected: foo, actually: bar");  // and take a screenshot
}

You see: the idea is really simple.

In reality, this code is a bit more complex. It’s because it’s “generic” - not only for shouldBe(visible), but for all other methods and conditions.

As you know,

the devil is in the details

In the code shown above, there is plenty of questions:

  1. Which exceptions to catch?
    • Exception, Error, Throwable, AssertionError, WebDriverException?
  2. In case of which exceptions should we stop the waiting and fail the test immediately?
    • for example, if XPath is invalid, it will remain invalid after 4 seconds too.
  3. The result is ok or nok?
    • for example, if element is not found - it could be ok for condition $.shouldNot(exist).
  4. At what moment would we take screenshot?
  5. Can user customize any of these lines?
    • For example, it’s probably not needed to take a screenshot because Allure will take its own screenshot anyway.
    • Or the opposite, we probably should take screenshot and pass it to Allure somehow?
    • (currently both Selenide and Allure take a screenshot, so they are duplicated)
  6. What if we run until the last line, and during execution of the last line we got a fu#ng StaleElementException?

Our answers to these questions have been changing in time. And will probably change. But the essence remains.

What’s now?

I hope you will now understand Selenide waiting instead of perceiving it as a “black magic”. It will probably help you during debugging of some corner cases and mystical test failures.

And you can even suggest an idea how to improve or simplify the Skynet core Main Algorithm.


Andrei Solntsev

selenide.org

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