Re-executing failed test cases and merging outputs with Robot Framework

In a previous post, I discussed solving intermittent issues aka building more robust automated tests. A solution I did not mention is the simple “just give it another chance”. When you have big and long suites of automated tests (quite classic to have suites in the 1000’s and lasting hours when doing functional tests), then you might get a couple of tests randomly failing for unknown reasons. Why not just launching only those failed tests again? If they fail once more, you are hitting a real problem. If they succeed, you might have hit an intermittent problem and you might decide to just ignore it.

Re-executing failed tests (–rerunfailed) appeared in Robot Framework 2.8. And since version 2.8.4 a new option (–merge) was added to rebot to merge output from different runs. Like explained in the User Guide, those 2 options make a lot of sense when used together:

# first execute all tests
pybot --output original.xml tests 
# then re-execute failing
pybot --rerunfailed original.xml --output rerun.xml tests 
# finally merge results
rebot --merge original.xml rerun.xml

This will produce a single report where the second execution of the failed test is replacing the first execution. So every test appears once and for those executed twice, we see the first and second execution message:

modified

Here, I propose to go a little bit further and show how to use –rerunfailed and –merge while:

  • writing output files in an “output” folder instead of the execution one (use of –outputdir). This is quite a common practice to have the output files written in a custom folder but it makes the whole pybot call syntax a bit more complex.
  • giving access to log files from first and second executions via links displayed in the report (use of Metadata). Sometimes having the “new status” and “old status” (like in previous screenshot) is not enough and we want to have details on what went wrong in the execution, and having only the merged report is not enough.

To show this let’s use a simple unstable test:

*** Settings ***
Library  String

*** Test Cases ***
stable_test
    should be true  ${True}

unstable_test
    ${bool} =  random_boolean
    should be true  ${bool}
    
*** Keywords ***
random_boolean
    ${nb_string} =  generate random string  1  [NUMBERS]
    ${nb_int} =  convert to integer  ${nb_string}
    Run keyword and return  evaluate  (${nb_int} % 2) == 0

The unstable_test will fail 50% of times and the stable test will always succeed.

And so, here is the script I propose to launch the suite:

# clean previous output files
rm -f output/output.xml
rm -f output/rerun.xml
rm -f output/first_run_log.html
rm -f output/second_run_log.html
 
echo
echo "#######################################"
echo "# Running portfolio a first time      #"
echo "#######################################"
echo
pybot --outputdir output $@
 
# we stop the script here if all the tests were OK
if [ $? -eq 0 ]; then
	echo "we don't run the tests again as everything was OK on first try"
	exit 0	
fi
# otherwise we go for another round with the failing tests
 
# we keep a copy of the first log file
cp output/log.html  output/first_run_log.html
 
# we launch the tests that failed
echo
echo "#######################################"
echo "# Running again the tests that failed #"
echo "#######################################"
echo
pybot --outputdir output --nostatusrc --rerunfailed output/output.xml --output rerun.xml $@
# Robot Framework generates file rerun.xml
 
# we keep a copy of the second log file
cp output/log.html  output/second_run_log.html
 
# Merging output files
echo
echo "########################"
echo "# Merging output files #"
echo "########################"
echo
rebot --nostatusrc --outputdir output --output output.xml --merge output/output.xml  output/rerun.xml
# Robot Framework generates a new output.xml

and here is an example of execution (case where unstable test fails once and then succeeds):

$ ./launch_test_and_rerun.sh unstable_suite.robot

#######################################
# Running portfolio a first time      #
#######################################

==========================================================
Unstable Suite
==========================================================
stable_test                                       | PASS |
----------------------------------------------------------
unstable_test                                     | FAIL |
'False' should be true.
----------------------------------------------------------
Unstable Suite                                    | FAIL |
2 critical tests, 1 passed, 1 failed
2 tests total, 1 passed, 1 failed
==========================================================
Output:  path/to/output/output.xml
Log:     path/to/output/log.html
Report:  path/to/output/report.html

#######################################
# Running again the tests that failed #
#######################################

==========================================================
Unstable Suite
==========================================================
unstable_test                                     | PASS |
----------------------------------------------------------
Unstable Suite                                    | PASS |
1 critical test, 1 passed, 0 failed
1 test total, 1 passed, 0 failed
==========================================================
Output:  path/to/output/rerun.xml
Log:     path/to/output/log.html
Report:  path/to/output/report.html

########################
# Merging output files #
########################

Output:  path/to/output/output.xml
Log:     path/to/output/log.html
Report:  path/to/output/report.html

So, the first part is done: we have a script that launch the suite twice if needed and put all the output in “output” folder. Now let’s update the “settings” section of our test to include links to first and second run logs:

*** Settings ***
Library   String
Metadata  Log of First Run   [first_run_log.html|first_run_log.html]
Metadata  Log of Second Run  [second_run_log.html|second_run_log.html]

 If we launch our script again, we will get a report with links to first and second run in the “summary information” section:

report

The script and the test can be found in a GitHub repository. Feel free to comment on that topic if you found out more tips on those Robot options.

Visual Regression Tests

The first rule of “UI automated regression tests” is “You do not perform any UI automated regression tests”.

The second rule of “UI automated regression tests” is “In some contexts, if you really know what you are doing, then some automated regression tests performed via the UI can be relevant”.

Martin Fowler explained it very well in his Testing Pyramid article: “a common problem is that teams conflate the concepts of end-to-end tests, UI tests, and customer facing tests. These are all orthogonal characteristics. For example a rich javascript UI should have most of its UI behaviour tested with javascript unit tests using something like Jasmine”. So the top of a testing pyramid should be:

  • built on top of a portfolio of unit and service/component/api tests (that should include some tests focussed on the UI layer)
  • a (small) set of end-2-end tests performed via the GUI to check that we did not miss anything with our more focussed tests.

For those end-2-end tests, the usual suspect in the Open Source scene is Selenium. Driving the browser through our app via the most common paths is a good way to gain some final confidence on the SUT. But one should really understand that what Selenium will check is the presence of some elements on the page and the events associated with some elements. “if I fill this input box and click on that button then I expect to see a table with this and that strings in it”, but it does not check the visual aspect of the page. To put it another way, with Selenium we are checking the nervous system of our SUT, but not its skin. Here come the visual regression testing tools.

Thoughtworks Radar raised their level from “assess” to “trial” on “visual regression testing tools last July with this comment: “Growing complexity in web applications has increased the awareness that appearance should be tested in addition to functionality. This has given rise to a variety of visual regression testing tools, including CSS Critic, dpxdt, Huxley, PhantomCSS, and Wraith. Techniques range from straightforward assertions of CSS values to actual screenshot comparison. While this is a field still in active development we believe that testing for visual regressions should be added to Continuous Delivery pipelines.”

So I wanted to give it a try and did a quick survey of the tools available. I wanted to know which project were still active, what was their langage/ecosystem and what browser were supported. Here is list I just built:

My shopping list was:

  • Python, as I am already using Robot Framework in this langage
  • Support for another browser than PhantomJS because my SUT does not render very well under PhantomJS at the moment

So I chose needle which, according to its author is “still being maintained, but I no longer use it for anything”. I gave it a try and it works well indeed. I now have a basic smoke test trying to catch visual regression tests. More on that soon if I have more feedback to share.