C[omp]ute

From: andrew cooke <andrew@...>

Date: Wed, 11 Aug 2010 16:07:57 -0400

This is a follow-up to my earlier post on Selenium at
http://www.acooke.org/cute/SeleniumWe0.html - there I gave a summary of
Selenium and the basic tools needed to run simple, single tests.

However, what is interesting me at the moment (because we need it at work) is
how to run the same test in several browsers, on different operating systems.
This requires two things:

1 - A way to distribute jobs across machines
2 - A way to make tests general (the tests in the first article specified
    the target browser).

Selenium provides these things via something called "Selenium Grid", although
much of the documentation for that focuses on running tests in parallel (for
speed) rather than on exploiting different environments.

A warning: the Selenium Grid documentation sucks.  I have spent a frustrating
couple of days getting this working.  Even the demo they provide to test the
system doesn't work.  And the system itself seems a bit limited and
unreliable.  But, unfortunately, I don't see anything better.


OK, so what is Selenium Grid?  It's three things:

A - A central hub that manages a collection of servers
B - A collection of servers (possibly on remote machines)
C - Library support for writing tests

(A+B) address (1) above and (C) addresses (2).  This is all packaged in a Java
deploy and run using ant-based scripts.


First, I want to describe how the distribution of tasks works, because I found
this far from intuitive.  It's important to understand that all the servers
(called "remote controls") are equivalent and dumb.  They don't "know" that
they are running on Windows, or can access the Opera browser, for example.
The only way that such information is made available to the system is through
the *environment*.

When you start a server you specify its environment.  This is a string, and
the standard form is something like "IE on Windows" or "Firefox on Linux".
That information is passed by the server to the central hub which uses that
(and only that) to route tests.

The hub is also contacted by the test.  The test requests a particular
environment (I'll address 2/C below) and the hub then routes the test to the
corresponding server.


At this point it's probably worth describing exactly how these things run.
This is how I start the hub and a local server on Linux (first script uses
konsole as they log to stdout - although on Windows you don't see anything,
and I don't understand why):

  > cat startup-selenium.sh
  #!/bin/bash
  konsole --hold -e startup-hub.sh &
  sleep 5
  konsole --hold -e startup-rc.sh &

  > cat startup-hub.sh
  #!/bin/bash
  cd .../selenium-grid-1.0.6/
  ant launch-hub

  > cat startup-rc.sh
  #!/bin/bash
  cd .../selenium-grid-1.0.6/
  ant \
    -Dport=5555 \
    -Dhost=10.2.0.0 \
    -DhubURl=http://10.2.0.0:4444 \
    -Denvironment='Firefox on Linux' \
    launch-remote-control

You can see how the server's environment is defined as 'Firefox on Linux'.
Note also that the server is told the location of the hub so that it can
register itself.  You can see the hub's status by pointing a browser at
/console on the same URL (so http://10.2.0.0:444/console in my example above).


I can then run a test:

  > ant -Dbrowser="Firefox on Linux" run-in-sequence
  Buildfile: build.xml

  run-in-sequence:
       [java] [Parser] Running:
       [java]   Selenium Grid Tests In Sequence
       [java]
       [java] 11-Aug-2010 15:45:52 com.thoughtworks.selenium.grid.tools.ThreadSafeSeleniumSessionStorage startSeleniumSession
       [java] INFO: Contacting Selenium RC at 10.2.0.0:4444
       [java] 11-Aug-2010 15:45:59 com.thoughtworks.selenium.grid.tools.ThreadSafeSeleniumSessionStorage startSeleniumSession
       [java] INFO: Got Selenese session:com.thoughtworks.selenium.DefaultSelenium@...
       [java] 11-Aug-2010 15:46:16 com.thoughtworks.selenium.grid.tools.ThreadSafeSeleniumSessionStorage closeSeleniumSession
       [java] INFO: Closing Selenese session: com.thoughtworks.selenium.DefaultSelenium@...
       [java]
       [java] ===============================================
       [java] Selenium Grid Tests In Sequence
       [java] Total tests run: 1, Failures: 0, Skips: 0
       [java] ===============================================
       [java]

  BUILD SUCCESSFUL
  Total time: 23 seconds

I will explain how tests are written and structured, but first I need to add
one extra point.  There's an additional piece of information needed, which is
the "driver" used to run the tests.  This depends on the browser, and so we
need to map from environment to driver.  This is done in the file
grid_configuration.yaml in the main selenium-grid directory and displayed in
the hub console display.


So far I have addressed my point (1), but haven't really explain how (2) is
solved.  And in truth, I don't completely know - I am simply copying some code
that works.

However, I do know that the documentation is *particularly* poor on this, so
this information is critical.

First, the ant scripts use TestNG to run Java tests.  But the tests generated
by the IDE (export as Java TestNG) seem sot be using an old, unsupported
library.  Do *not* try hunting down the appropriate class and jar
(SeleneseTestNgHelper) because it does not work with the rest of the
(ant-based) environment, as far as I can see.

Instead, copy the supplied code used in the (broken!) tests in the Selenium
Grid package.  In particular, copy GoogleImageTestBase.java and compare ti to
the code generated by the IDE - it's pretty obvious how to do the translation.

Note that the libraries involved do the necessary work of somehow adapting the
tests to use the parameters supplied to any when invoking with a particular
environment.


If you do all that then you will need to link to the following jars:
  commons-logging-1.0.4.jar
  selenium-java-client-driver.jar
  testng-5.7-jdk15.jar
  selenium-server-1.0.3-standalone.jar
  selenium-grid-tools-standalone-1.0.6.jar

You will also need a build.xml that can compile that and run the test.  I
used:

  <project name="..." basedir=".">

    <property name="src.dir"     value="${basedir}/src"/>
    <property name="classes.dir" value="${basedir}/classes"/>
    <property name="lib.dir"     value="${basedir}/lib"/>

    <path id="classpath">
      <fileset dir="${lib.dir}" includes="**/*.jar"/>
      <pathelement path="${classes.dir}"/>
    </path>

    <target name="compile">
      <mkdir dir="${classes.dir}"/>
      <javac srcdir="${src.dir}" destdir="${classes.dir}" classpathref="classpath"/>
    </target>

    <property name="webSite" value="http://10.2.0.0:8080/" />
    <property name="seleniumHost" value="10.2.0.0" />
    <property name="seleniumPort" value="4444" />
    <property name="browser" value="*firefox" />

    <target name="run-in-sequence" description="Run Selenium tests one by one">
      <java classpathref="classpath"
            classname="org.testng.TestNG"
                failonerror="true">
            <sysproperty key="java.security.policy" file="${basedir}/lib/testng.policy"/>
            <sysproperty key="webSite" value="${webSite}" /> 
            <sysproperty key="seleniumHost" value="${seleniumHost}" />
            <sysproperty key="seleniumPort" value="${seleniumPort}" /> 
            <sysproperty key="browser" value="${browser}" /> 

        <arg value="-suitename" />
        <arg value="Selenium Grid Tests In Sequence" />
        <arg value="-d" />
        <arg value="${basedir}/target/reports" />
        <arg value="-testclass"/>
        <arg value="MyClass"/>
      </java>
    </target>

  </project>

which is just a simple copy of the one supplied in the grid package.


I hope that helps!

Andrew