Web Application Testing with Selenium
At first glance, it looks like Selenium RC supports enough parallelism that any additional distributed processing capability would not be needed. After all, a single Selenium RC server allows you to open a number of parallel sessions (that is, drive a number of browsers at the same time) and a single Selenium RC client. In addition to being able to work with multiple concurrent sessions of one server, it can communicate with multiple servers at the same time.
However, in practice, running more than six browsers on the same Selenium RC server is not advisable due to performance issues. Additionally, managing a large number of Selenium RC servers is a major headache and does not scale very well. This is where Selenium Grid can help.
Selenium Grid introduces another component to the Selenium architecture—Selenium Hub, which manages a pool of available Selenium Remote Control entities and is responsible for the following:
Transparently allocating a Selenium RC entity to a specific test.
Limiting the number of concurrent test runs on each Remote Control.
Shielding the tests from the actual grid infrastructure.
As far as your RC client programming is concerned, the move from Selenium RC to Grid requires minimal code changes. All you have to do is to change the infamous browser string parameter. For instance, change "*firefox" to something like "Firefox on Windows" or "Safari on Mac".
Selenium Hub's configuration is a bit more complex. First, you have to modify the grid_configuration.yml file. Let's say you want to use two RC instances—one with Firefox on Linux and another with Internet Explorer on Windows. In that case, your configuration file will look like this:
hub: port: 4444 environments: - name: "Firefox on Linux" browser: "*firefox" - name: "IE on Windows" browser: "*iexplore"
After that, you should use ant to launch the Selenium Hub by running ant launch-hub on the hub machine. The RC instances are created by running the following commands, one on a Linux machine and one on a Windows machine.
On the Linux machine:
ant -Denvironment="Firefox on Linux" \ -DhubURL=http://<hub-IP-address>:4444 \ launch-remote-control
On the Windows machine:
ant -Denvironment="IE on Windows" \ -DhubURL=http://<hub-IP-address>:4444 \ launch-remote-control
After that, you can code your RC client to use any of the above RC server instances via the hub.
Comprehensive description of the Selenium API is beyond the scope of this article, but the list below demonstrates what the framework is capable of:
$sel->click($locator) — Clicks on a link, button, check box or radio button.
$sel->context_menu($locator) — Simulates opening the context menu for the specified element (as might happen if a user right-clicks on the element).
$sel->focus($locator) — Moves the focus to the specified element.
$sel->key_press($locator, $key_sequence) — Simulates a user pressing and releasing a key.
$sel->mouse_over($locator) — Simulates a user hovering the mouse over the specified element.
$sel->type($locator, $value) — Sets the value of an input field, as though you typed it in.
$sel->check($locator) — Checks a toggle button (check box/radio).
$sel->select($select_locator, $option_locator) — Selects an option from a drop-down menu using an option locator.
$sel->submit($form_locator) — Submits the specified form.
$sel->open($url) — Opens a URL in the test frame.
$sel->open_window($url, $window_id) — Opens a pop-up window.
$sel->go_back() — Simulates a user clicking the back button in the browser.
$sel->get_location() — Gets the absolute URL of the current page.
$sel->get_body_text() — Gets the entire text of the page.
$sel->get_text($locator) — Gets the text of an element.
$sel->get_selected_indexes($select_locator) — Gets all option indexes for the selected options in the specified select or multi-select element.
$sel->get_all_links() — Returns the IDs of all links on the page.
$sel->get_cookie() — Returns all cookies for the current page under test.
$sel->wait_for_text_present($text, $timeout) — Waits until $text is present in the HTML source.
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