Selenium RC

Selenium RCoff of your desktopand onto the grid

Jennifer Bevan & Jason Huggins{jbevan, hugs}@google.com

Google, Inc.August 24, 2007

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What we have to share…

• Experience report on extending Selenium RC from desktopuse to running within a grid.

• Demo: “gridified” (© jason) Selenium RC for the masses.

– You don’t have to be Google to parallelize your selenium tests

• Future directions & addressing needs.

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Background

• Selenium RC (org.openqa.selenium) uses javascript to interactwith browsers.

– Provides ability to inspect contents of pages programmatically.

– Executes only within the scope of a browser session.

• Can’t handle all modal dialog windows:

– File upload

– File download

– Browser crash report

– Supports injection “of large chunks of badly written javascript”[S. Stewart, GTAC’07] into the page.

• Google has created a “farm” of Selenium RC machines thatfacilitates parallelized testing of multiple configurations.

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High-level Architecture

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A couple of usage statistics…

• Over 10 projects’automated/continuous test systems,and many(uncounted)individual users.

• Gmail tests,running at 1thread/test, wentfrom taking over40 minutes to 3.5minutes

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Experience Report

• We discovered many different issues while deploying andduring adoption of the Google Selenium RC farm.

– Browser/OS variances in configuration and capabilities

– Reliability and scalability issues

– Limitations that are out of the execution context of SeleniumRC

• Changes we make to Selenium RC to support our needs getpropagated to the open source repository.

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Browser/OS Issues

• Top issue: test isolation

– Firefox: RC generates a user profile specific to a test session.

– IE: RC modifies registry settings and configures the LANconnection settings directly.

• Therefore, either IE tests must be externally isolated(individual VMs, single-tracked, etc.) or RC needs to manageaccess to the shared resources.

– The latter approach not used in current RC code.

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Browser/OS Issues (cont.)

• Javascript evaluation within the browser

– Firefox (*chrome) allows tests to bypass security checks inspecific situations

– IE (*iehta) is expected to perform similarly, but isexperimental within Selenium RC.

• Therefore, we’ve only deployed *iexplore

• Basic tests (no https, etc.) are not a problem.

• Complex tests that work in *chrome are not immediatelyusable on *iehta.

• Limits ability to immediately test multiple configurations(requires test modification)

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Reliability Issues

• When we initially deployed our Selenium RC farm, thedeadlock in the current RC code was not known.

– Concurrently, ongoing work on RC increased deadlockrate, resulting in a wider awareness.

• Is not related to browser type or test complexity, so allusers experience spurious test failures.

– Defensive strategy: retry failed tests

• Google and the Selenium RC development team areactively addressing this problem (top priority).

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Reliability Issues (cont.)

• Selenium RC has a memory leak and a connection leak.

• We adopted a two-prong approach for this.

– Defensive strategy: periodically drain off tests and restart RC

– Offensive strategy: search and destroy source of leaks.

• Defensive strategy works, so for right now this is not our toppriority.

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Reliability Issues (more)

• Current Selenium RC regression test suite contains bothfunctional and unit tests.

– And yet, most of them are “happy path” (© patrick) tests.

– All of the issues we’ve found were in code that passed theRC regression tests.

– Resulting uncertainty affects ability to quickly deploy newversions (with new RC features) on the farm.

• We are contributing tests to the open source repositorythat better exercises our new code and the surroundingpre-existing code.

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Scalability Issues

• Session identification

– Current RC code uses a method of identifying sessions that isbased solely on time.

• For our purposes, this was not unique enough.

• Patch to improve uniqueness made, will be given to opensource repository.

• Multiple tests per RC instance

– Unofficial assumption by RC development team that eachsession is in an isolated VM.

• We are considering tradeoffs between this model and addingfull support for concurrent tests in one machine.

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What about Performance?

• Sure -- making RC faster would be great.

– We’re focusing on fixes that affect RC’s “gridability”: reliability andscalability

– Also, the point of creating a grid is to make all of your tests run inthe amount of time it takes your longest test to run.

• At which point performance fixes get more attention.

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Other contributions…

• Exposed bug in handling of InterruptedException withinSelenium RC.

– A waitFor…(elementName, 45000) statement “timed out” inunder 4 seconds, not 45 seconds.

– Added fix and tests for timeout calculation.

• Exposed tendency of Selenium RC to leave browsers openafter test session has ended.

– Usually when a test enters a deadlock or when a javascript “eval”stops responding.

– Current effort focused on eliminating deadlock; followup work willstrengthen browser shutdown method.

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Out-of-scope RC limitations

• A grid of Selenium RC machines is not something you want tomaintain manually.

– So if IE “encounters an error” and gets wedged to the pointwhere no new IE session can be started…” -- do you reallywant to VNC in and click “Don’t Send” to clear the IE state?

• Out-of-band communication with a farm manager to handleplatform-specific browser error handling is necessary for large-scale deployment.

– And once you have the requisite ‘watchdog’ client on the RCmachine, you can also use it for metric collection, managingconfiguration recovery, etc…

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(and now we switch to Jason…)

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Which is faster? (1 server, sequential tasks)

Time

Servers

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3

4

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Which is faster? (4 servers, parallel tasks)

Time

Servers

1

2

3

4

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How do you add more servers?

Thank this dude

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Make computing a true utility (for anyone)

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Pricing is cheap, but it’s not free.

$.10 per hour

==

~$74 per month

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Demo…

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Questions?

1. Are you going to open-source this?

2. Who is Paul Hammant?(http://paulhammant.com/)

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Creator of Selenium Driven aka “Remote Control”

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Thank you, Paul. :-)