Selenium Error: no display specified - firefox

Question

I've installed selenium-server-standalone-2.42.2.jar in a debian virtual box
and installed Firefox 29.0
and trying to run the following script with phpunit which is the only file in the directory:
<?php
class TestLogin extends PHPUnit_Extensions_Selenium2TestCase{
public function setUp()
{
$this->setHost('localhost');
$this->setPort(4444);
$this->setBrowser('firefox');
$this->setBrowserUrl('http://debian-vm/phpUnitTutorial');
}
public function testHasLoginForm()
{
$this->url('index.php');
$username = $this->byName('username');
$password = $this->byName('password');
$this->assertEquals('', $username->value());
$this->assertEquals('', $password->value());
}
}
I get the following error:
1) TestLogin::testHasLoginForm
PHPUnit_Extensions_Selenium2TestCase_WebDriverException: Unable to connect to host
127.0.0.1 on port 7055 after 45000 ms. Firefox console output:
Error: no display specified
Error: no display specified
What does this mean?
I've red several threads and apparently I had to do the following which I tried:
1)to type this in the command shell
export PATH=:0;
Result: I got the same error.
2) I've installed vnc4server and getting debian-vm:1 as a application I then set export PATH=debian-vm:1 run it with realvnc and in the viewer (which works) I got the same problem.

Answer 1

You receive this error, because you have not set the DISPLAY variable. Here is a guide how to perform the test on a headless machine.
You have to install Xvfb and a browser first:
apt-get install xvfb
apt-get install firefox-mozilla-build
then start Xvfb:
Xvfb &
set DISPLAY and start Selenium:
export DISPLAY=localhost:0.0
java -jar selenium-server-standalone-2.44.0.jar
and then you will be able to run your tests.

Answer 2

These days setting up headless is as easy as passing an option to the selenium browser driver.
On most environments this can be done by setting the env variable MOZ_HEADLESS before running your tests, i.e try:
export MOZ_HEADLESS=1
Then, rerun your tests and it should run headless.
If you're out of luck, and it doesn't pick up the env var, try enabling the headless support in the driver config. E.g: with phpunit-selenium lib, do this:
Firefox
$this->setDesiredCapabilities(['moz:firefoxOptions'=> ['args' => ['-headless']]]);
Chrome
$this->setDesiredCapabilities(['chromeOptions'=>['args'=>['headless']]]);
See php-webdriver wiki for more selenium options.

Answer 3

Certainly scripting is the way to go, however iterating through all possible DISPLAY values is not as good as using the right DISPLAY value. Also there is no need for xvfb at least in debian/ubuntu. Selenium can be run locally or remotely using a current DISPLAY session variable as long as it is correct. See my post in http://thinkinginsoftware.blogspot.com/2015/02/setting-display-variable-to-avoid-no.html but in short:
# Check current DISPLAY value
$ echo $DISPLAY
:0
# If xclock fails as below the variable is incorrect
$ xclock
No protocol specified
No protocol specified
Error: Can't open display: :0
# Find the correct value for the current user session
$ xauth list|grep `uname -n`
uselenium/unix:10 MIT-MAGIC-COOKIE-1 48531d0fefcd0a9bde13c4b2f5790a72
# Export with correct value
$ export DISPLAY=:10
# Now xclock runs
$ xclock

Answer 4

The following is not the right variable:
$ export PATH=:0;
That defines where to find executables, such as in /bin, /usr/local/bin.
You're working with X11 variants and in that context, :0 refers to DISPLAY localhost:0.
So you probably intended the following:
$ export DISPLAY=:0
But as others have pointed out there needs to actually be an Xserver (virtual or otherwise) at that DISPLAY address. You can't just make up a value and hope it will work.
To find a list of DISPLAYs that your user is authorized to connect to you can use the following, then set your DISPLAY variable according (host:displayNumber, or :displayNumber if on the local host):
$ xauth list