dim_brightness test would return 1 even it works due to the potential rounding issue

[Po-Hsu Lin]

Expected result:
dim_brightness script would return 0 to make the test pass, and brightness successfully dimmed.

Actual result:
It return 1, but brightness successfully dimmed.
Tested on 201306-13745

It looks like the script didn't pass the if statement in the brightness value checking algorithm:
    def was_brightness_applied(self, interface):
        '''See if the selected brightness was applied

        Note: this doesn't guarantee that screen brightness
              changed.
        '''
        if (self.get_actual_brightness(interface) !=
            self.get_last_set_brightness(interface)):
            return False
        else:
            return True

root@201306-13745:~$ apt-cache policy checkbox
checkbox:
  Installed: (none)
  Candidate: 0.18-0ubuntu2
  Version table:
     0.18-0ubuntu2 0
        500 http://archive.ubuntu.com/ubuntu/ vivid/universe amd64 Packages
root@201306-13745:~$ apt-cache policy plainbox
plainbox:
  Installed: 0.22+bzr3836+pkg29~ubuntu15.04.1
  Candidate: 0.22+bzr3836+pkg29~ubuntu15.04.1
  Version table:
 *** 0.22+bzr3836+pkg29~ubuntu15.04.1 0
        500 http://ppa.launchpad.net/checkbox-dev/ppa/ubuntu/ vivid/main amd64 Packages
        100 /var/lib/dpkg/status
     0.5.4-1 0
        500 http://archive.ubuntu.com/ubuntu/ vivid/universe amd64 Packages
root@201306-13745:~$ plainbox dev list provider
provider '2013.com.canonical.plainbox:manifest'
provider '2013.com.canonical.plainbox:categories'
provider '2013.com.canonical.certification:certification-client'
provider '2013.com.canonical.certification:checkbox'
provider '2013.com.canonical.certification:plainbox-resources'
provider '2013.com.canonical.certification:piglit'

[Po-Hsu Lin (cypressyew)]

On a 14.04.3 I+A system (201404-14986), the dim_brightness script return 1 because of the brightness value checking algorithm mentioned above.
After running the script on this system, the brightness will be changed from 5273 to 2636, but the actual brightness is 2637. Therefore it's causing this issue.

We should double check this on other system to see how the rounding works.

[Po-Hsu Lin (cypressyew)]

On 201407-15273, 14.04.3 + 4.2 kernel, I can reproduce this, and the same rounding issue can be found there.
The brightness will be changed from 937 to 468, but the actual brightness will is 469.

[Po-Hsu Lin (cypressyew)]

On 201401-14542, 14.04.1 (3.13.0-63), although the maximum brightness is 937, however both of the brightness and actual_brightness will be changed to 468. So it won't return FAIL on this system.

Looks like we can't just round it.

[Po-Hsu Lin (cypressyew)]

So for comment #2 and #3, we could obtain the same value from our script (937/2=468), it's the actual brightness that is causing the problem.

A quick and dirty fix is to add a tolerance value or percentage, e.g. make it pass with actual brightness = 468 +/- 1

[Vanessa Chang (vanessa-chang)]

this issue can also be reproduced during oem project testing. add tag accordingly.