Running UI tests on Travis

2018-06-07T00:00:00-03:00

Travis allows you to run Chrome and Firefox on their build environment and those can be used to run UI tests using Selenium.

Today we are going to see how to install chromedriver and geckodriver in order to be able to run UI tests using pytest-selenium. To run those tests you will need to have your web application running so that Travis can access it and this article won't cover that.

Assuming that you already have Travis setup for your project, the first step to do is to enable the Chrome and Firefox addons. You can do that by adding the following lines to your .travis.yml file:

addons:
  chrome: stable
  firefox: latest

Those lines will make Travis make available both Chrome and Firefox but that won't install neither chromedrive and geckodriver which are required to run Selenium webdriver. To make the process of setting up them, let's create some scripts.

First create the setup_chromedriver.sh script:

#!/bin/bash
set -euvo pipefail

export LATEST_CHROMEDRIVER="$(curl -s https://chromedriver.storage.googleapis.com/LATEST_RELEASE)"
curl -L -s -o /tmp/chromedriver.zip "https://chromedriver.storage.googleapis.com/${LATEST_CHROMEDRIVER}/chromedriver_linux64.zip"
mkdir "${HOME}/chromedriver"
unzip /tmp/chromedriver.zip -d "${HOME}/chromedriver"

The script is checking for the latest chromedriver and downloading it. Next it creates a diretory where the chromedriver executable will be placed. We are creating a directory because later we will be adding that directory to the PATH.

Next is time to create the setup_geckodriver.sh script:

#!/bin/bash
set -euvo pipefail

curl -L -s -o geckodriverrelease https://api.github.com/repos/mozilla/geckodriver/releases/latest

cat > parser.py <<EOF
import sys, json
r = json.load(sys.stdin)
if 'assets' in r:
    print([a for a in r['assets'] if 'linux64' in a['name']][0]['browser_download_url']);
else:
    print('https://github.com/mozilla/geckodriver/releases/download/v0.20.1/geckodriver-v0.20.1-linux64.tar.gz')
EOF

export GECKODRIVER_DOWNLOAD="$(cat geckodriverrelease | python parser.py)"
curl -L -s -o /tmp/geckodriver.tar.gz "${GECKODRIVER_DOWNLOAD}"

mkdir "${HOME}/geckodriver"
tar xvf /tmp/geckodriver.tar.gz -C "${HOME}/geckodriver"

As you can see, to install the latest geckodriver it requires some extra logic. See below a detailed explanation about why that is required.

geckodriver is hosted on Github and you can get the latest release information using Github's API. The script is fetching that information by doing an unauthenticated request. The problem with unauthenticated requests to Github's API is that it limits, currently, to 60 requests per hour. Even though your project's tests may run once a day you can hit that request limit because the Travis environment is shared.

To avoid the hitting the request rate limit and to parse the information about the latest limit the script is creating the parser.py Python script that will fetch the URL for the latest release by parsing the JSON response (saved on geckodriverrelease file by curl) or default to the current latest release URL if the Github API's rate limite is hit.

After fetching the proper URL to download the latest geckodriver the script go ahead and get it and place it on the created geckodriver directory. Same as chromedriver this directory will be added later to the PATH.

With all that in place, it is time to edit the .travis.yml file again and make it run the UI tests. In the example we are going to see here, both setup scripts were placed into a scripts directory on the projects repository's root directory.

To make it more visually appealing on Travis let's run UI tests using build stages. Below are the definitions for the jobs to run tests using both Chrome and Firefox on separated jobs. The environment variable NAME is there just provide context on Travis UI since you can't set jobs name as of now. On the before_install section of each job is where chromedriver and geckodriver are setup and the executables are added to the PATH. Finally the tests are running on the script section using xvfb-run which is required to run the browsers in headless mode.

- stage: test-ui
  env:
    - NAME=ui-chrome
  before_install:
    - ./scripts/setup_chromedriver.sh
    - export PATH="${HOME}/chromedriver:${PATH}"
    - chromedriver --version
  install:
    - make run-web-app
  script:
    - xvfb-run py.test -v --driver Chrome path/to/ui/tests

- stage: test-ui
  env:
    - NAME=ui-firefox
  before_install:
    - ./scripts/setup_geckodriver.sh
    - export PATH="${HOME}/geckodriver:${PATH}"
    - geckodriver --version
  install:
    - make run-web-app
  script:
    - xvfb-run py.test -v --driver Firefox path/to/ui/tests

After all that you should be able to run UI tests on Travis. If you want a full .travis.yml example you can check integrade's .travis.yml.

Using a C shared library with Python's ctypes module

2018-03-09T00:00:00-03:00

To demonstrate how to create a shared C library and using it with Python's ctypes library we are going to create a shared C library. First create the C header file mean.h:

// Returns the mean of passed parameters
double mean(double, double);

Next create the C file mean.c:

#include "mean.h"

double mean(double a, double b) {
    return (a+b)/2;
}

Now we can create the shared C library by compiling it using gcc:

$ gcc -shared -o libmean.so.1 mean.c

Finally we can import the shared C library using the ctypes Python module, consider the following interative shell:

>>> import ctypes
>>> libmean = ctypes.CDLL('./libmean.so.1') # loads the shared library
>>> libmean.mean.restype = ctypes.c_double # define mean function return type
>>> libmean.mean(ctypes.c_double(10), ctypes.c_double(3)) # call mean function needs cast arg types
6.5
>>> libmean.mean.argtypes = [ctypes.c_double, ctypes.c_double] # define arguments types
>>> libmean.mean(10, 3) # call mean function does not need cast arg types
6.5
>>> type(libmean.mean(10, 5)) # returned value is converted to python types
<class 'float'>

This was tested using Python 3.6.4 and gcc 7.3.1 on Fedora 27. Check the ctypes documentation for more information.

Elyézer Rezende

Running UI tests on Travis

Using a C shared library with Python's ctypes module