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Continuous Integration

Continuous Integration (CI) is a software development practice where quality control is continuously applied to the product as opposed to the traditional procedure of applying quality control after completing all development (during the so called integration phase). In essence, it is a way of decreasing the risks associated with the integration by spreading required efforts over time, which helps to improve on the quality of software, and to reduce the time taken to deliver it.

Stringent quality control is particularly important in the context of NEST, a neuronal network simulator with the emphasis on correctness, reproducibility and performance. However, given the limited amount of the available resources, it is wasteful to transfer the responsibility to re-run the test suite for all target platforms on every single code base change to the shoulders of the developers.

In order to address this problem, a Travis-Continuous Integration (CI) service has been setup, which would allow for regular testing of changes that are getting into the tree and timely reporting of identified problems. This way, issues will be discovered earlier and the amount of efforts to fix them will be significantly decreased (hopefully). Continuous Integration at NEST Simulator

The current CI implementation is now available at the following URL: https://travis-ci.org/nest/nest-simulator. Travis CI service has been integrated with the Github repository to automatically run the tests when code is pushed. Github integration is done by adding a simple YAML file to the project root.Travis results will appear in the Github pull requests and the primary log is visible in the Travis interface.

Build jobs

The CI system is closely integrated to Github repository. Whenever some changes in the code are detected, the latest source code is downloaded to a worker machine which is running on Ubuntu 14.04 LTS(Trusty) and the following actions are performed:

  • Bootstrap the build system
  • Build and install NEST
  • Run the test suite
  • Uploading the build artifacts to Amazon S3 (Simple Storage Service) in case of merge commits to the master branch.

If any of the first three steps fails (returns a non-zero exit code), the build is marked as failed and a notification is sent to the person who initiated the build.

Pull Requests

Pull requests can be initiated by anyone having the fork of the repository. Travis builds only the pull requests from someone who has write access to the main repository. Rather than testing the commits from the branches the pull request is sent from, Travis test the merge between the origin and the upstream branch.

Uploading of artifacts to S3 is not allowed for the pull requests. From a pull request, the secure environment values (for e.g.: the encrypted access keys for S3) could not be extracted properly and thus the artifacts can’t be uploaded to S3. Secure access keys are set for the particular repository (in our case, nest/nest-simulator). Because of this reason, artifacts will be uploaded only when we merge the commit to the upstream master.

Skipping a Travis build

In the case of some changes in the documentation where you don’t want to trigger a Travis build, add [ci skip] or [skip ci] anywhere in the commit message.

Further reading