7.4.1 Choosing a Location Strategy
There are multiple ways of selecting an object on a page. But what are the trade offs of each of these locator types? Recall we can locate an object using
• the element’s ID
• the element’s name attribute • an XPath statement
• by a links text
• document object model (DOM)
Using an element ID or name locator is the most efficient in terms of test performance, and also makes your test code more readable, assuming the ID or name within the page source is well-named. XPath statements take longer to process since the browser must run its XPath processor. XPath has been known to be especially slow in Internet Explorer version 7. Locating via a link’s text is often convenient and performs well. This technique is specific to links though. Also, if the link text is likely to change frequently, locating by the <a> element would be the better choice.
Sometimes though, you must use an XPath locator. If the page source does not have an ID or name attribute you may have no choice but to use an XPath locator. (DOM locators are no longer commonly used since XPath can do everything they can and more. DOM locators are available simply to support legacy tests.)
There is an advantage to using XPath that locating via ID or name attributes do not have. With XPath (and DOM) you can locate an object with respect to another object on the page. For example, if there is a link that must occur within the second paragraph within a <div> section, you can use XPath to specify this. With ID and name locators, you can only specify that they occur on the page that is, somewhere on the page. If you must test that an image displaying the company logo appears at the top of the page within a header section XPath may be the better locator.
7.4.2 Locating Dynamic Elements
As was described earlier in the section on types of tests, a dynamic element is a page element whose identifer varies with each instance of the page. For example,
<a class="button" id="adminHomeForm" onclick="return oamSubmitForm(’adminHomeForm’, ’adminHomeForm:_ID38’);" href="#">View Archived Allocation Events</a>
This HTML anchor tag defines a button with an ID attribute of “adminHomeForm”. It’s a fairly complex anchor tag when compared to most HTML tags, but it is still a static tag. The HTML will be the same each time this page is loaded in the browser. Its ID remains constant with all instances of this page. That is, when this page is displayed, this UI element will always have this Identifier. So, for your test script to click this button you simply need to use the following selenium command.
click adminHomeForm
Or, in Selenium 1.0
Selenium Documentation, Release 1.0
selenium.click("adminHomeForm");
Your application, however, may generate HTML dynamically where the identifier varies on different instances of the webpage. For instance, HTML for a dynamic page element might look like this.
<input type="checkbox" value="true" id="addForm:_ID74:_ID75:0:_ID79:0:checkBox" name="addForm:_ID74:_ID75:0:_ID79:0:checkBox"/>
This defines a checkbox. Its ID and name attributes (both addForm:_ID74:_ID75:0:_ID79:0:checkBox) are dynamically generated values. In this case, using a standard locator would look something like the following.
click addForm:_ID74:_ID75:0:_ID79:0:checkBox
Or, again in Selenium-RC
selenium.click("addForm:_ID74:_ID75:0:_ID79:0:checkBox");
Given the dynamically generated Identifier, this approach would not work. The next time this page is loaded the Identifier will be a different value from the one used in the Selenium command and therefore, will not be found. The click operation will fail with an “element not found” error.
To correct this, a simple solution would be to just use an XPath locator rather than trying to use an ID locator. So, for the checkbox you can simply use
click //input
Or, if it is not the first input element on the page (which it likely is not) try a more detailed XPath statement.
click //input[3]
Or
click //div/p[2]/input[3]
If however, you do need to use the ID to locate the element, a different solution is needed. You can capture this ID from the website before you use it in a Selenium command. It can be done like this.
String[] checkboxids = selenium.getAllFields(); // Collect all input IDs on page.
for(String checkboxid:checkboxids) {
if(checkboxid.contains("addForm")) { selenium.click(expectedText);
} }
This approach will work if there is only one check box whose ID has the text ‘expectedText’ appended to it.
7.4.3 Locating Ajax Elements
As was presented in the Test Types subsection above, a page element implemented with Ajax is an element that can be dynamically refreshed without having to refresh the entire page. The best way to locate and verify an Ajax element is to use the Selenium 2.0 WebDriver API. It was specifically designed to address testing of Ajax elements where Selenium 1 has some limitations.
In Selenim 2.0 you use the waitFor() method to wait for a page element to become available. The parameter is a By object which is how WebDriver implements locators. This is explained in detail in the WebDriver chapters.
To do this with Selenium 1.0 (Selenium-RC) a bit more coding is involved, but it isn’t difficult. The approach is to check for the element, if it’s not available wait for a predefined period and then again recheck it. This is then executed with a loop with a predetermined time-out terminating the loop if the element isn’t found.
Let’s consider a page which brings a link (link=ajaxLink) on click of a button on page (without refreshing the page) This could be handled by Selenium using a for loop.
// Loop initialization.
for (int second = 0;; second++) {
// If loop is reached 60 seconds then break the loop.
if (second >= 60) break;
// Search for element "link=ajaxLink" and if available then break loop.
try { if (selenium.isElementPresent("link=ajaxLink")) break; } catch (Exception e) {}
// Pause for 1 second.
Thread.sleep(1000); }
This certainly isn’t the only solution. Ajax is a common topic in the user forum and we recommend searching previous discussions to see what others have done.