Continuous Integration (CI)
How can you know that changes to your files won’t break anything? Particularly when you start having large numbers of people making and merging changes, and sending you large numbers of pull requests?
One way would be to read every single line of text and manually review each change as they come in. However, as projects get bigger, and the number of people working together increases, this becomes an ever bigger and unmanagable task.
Instead, a better approach is to find a way of automatically testing every single change committed to the repository. If all of the tests pass, then you have confidence that nothing has been broken (assuming that you have good coverage with your tests). This approach, of automatically running tests on every commit, is called “continuous integration”, or CI.
GitHub is brilliant and useful because it has a built in link to a free CI platform called Travis CI. Travis CI provides free servers on which you can sync GitHub repositories and run tests. To use Travis CI, sign up for a Travis account and then next to the “My Repositories” link, click the “+” sign, e.g.
Travis CI links to your GitHub account, so knows all about your
repositories. Click the toggle switch to switch on CI testing
Next, to use Travis, you have to add a file called
to the top level of your
versioned_dir directory. Change
into this directory
cd cd versioned_dir
and then create the file using nano
Copy into the file the following
language: python python: - "3.5" # command to run tests script: python test.py
This file tells Travis that you want it to run a test script (which we will soon write)
test.py. This is run using the 3.5 version of the python interpreter (Travis
supports a lot of languages and versions. Take a look
here for the full documentation).
Next, create the
test.py test script
and copy in the text
lines = open("README.MD", "r").readlines() for line in lines: print(line, end="") print("\nEverything is OK")
This is a simple python script that just prints out every line of
and then prints
Everything is OK. Note that a good test script should
actually run some real tests… This is just for demonstration.
Add these two new files to Git and then commit and push your changes.
git add .travis.yml test.py git commit -a git push
Now, take a look at your Travis CI page, at
USERNAME is your GitHub/Travis username. For example,
my page is shown below.
You should see, as above, that Travis has seen the commit, has downloaded
and install Python, cloned your repository, and then run the
You should be able to see all of the output from
test.py, including that
the test passed, because
test.py exited with an exit value of 0 (a non-zero
exit value implies failure).
Showing Travis status on Github
To show the Travis build status on Github, you need to edit your
README.MD file. Open this up
and set the contents equal to
# Versioned Directory [ ![Travis Build Status](https://travis-ci.org/chryswoods/versioned_dir.svg?branch=master) ] (https://travis-ci.org/chryswoods/versioned_dir) # Hello Brilliant, Useful GitHub This is a README.MD file that will be used to describe this repository on GitHub This is a much improved introduction that includes a new list of items * Item 1 * Item 2 * Item 3 This is an extra line of text added to the copy of README.MD in the cloned repository
The first added lines just create a nice title for your project.
The next line
[ ![Travis Build Status](https://travis-ci.org/USERNAME/versioned_dir.svg?branch=master) ] (https://travis-ci.org/USERNAME/versioned_dir)
creates a markdown link to your Travis CI page for
versioned_dir, and uses the
image created for your Travis build status as the icon. Note that you will have
USERNAME with your Github/Travis username, e.g. for me, I have
[ ![Travis Build Status](https://travis-ci.org/chryswoods/versioned_dir.svg?branch=master) ] (https://travis-ci.org/chryswoods/versioned_dir)
Now go to your Github project page, and you should see a Travis icon
in your rendered
Skipping CI for some commits
Every time anyone now commits, the changes will be tested using Travis.
Sometimes you may only want to commit a small change, and don’t want the
test to run. If this is the case, ensure that the line
[ci skip] is included
in your commit message.
Deliberately break your
test.py script so that it exits with a non-zero
exit code. For example, you could use
import sys sys.exit(-1)
Commit your change and push it to Github. Watch what happens on Travis. What does a build fail look like?