Technical Details

On this page, we describe the challenges and technicalities of mining Travis CI and linking it to GitHub data poses several difficulties:

  • The official Ruby client is ill-suited for batch-acquiring logs (both due to a resource leak and because it does not fetch all logs).
  • Establishing a connection between GitHub and Travis CI build logs is all but trivial.

In particular, we have to deal with the issues of efficiently collecting data, build linearization and mapping, detailed in the following sections.

Data Collection

TravisPoker. To find out which and how many projects on GitHub use Travis, we implemented TravisPoker. This fast and lightweight application takes a GitHub project name as input (for example, rails/rails), and finds out if and how many Travis builds were executed for this project.

TravisHarvester. We implemented TravisHarvester to aggregate detailed information about a project’s Travis build history. It takes as input a GitHub project name and gathers general statistics on each build in the project’s history in a CSV file. Associated with each build entry in the CSV are the SHA1 hash of the Git commit, the branch and (if applicable) pull request on which the build was executed, the overall build status, the duration and starting time and the sub jobs that Travis executed for the different specified environments (at least one job, possibly many for each build). TravisHarvester downloads the build logs for each build for all jobs and stores them alongside the CSV file.

While both TravisPoker and TravisHarvester utilize Travis CI’s Ruby client for querying the API, we cannot use its job log retrieval function (Job:log) due to a memory leak (reported) and because it does not retrieve all build logs. We circumvented these problems by also querying an Amazon Cloud server we discovered that archives build logs.

To speed up the process of retrieving thousands of log files for each project, we parallelize our starter scripts for TravisHarvester with GNU Parallel.

Analysis of Build Logs

BuildAnalyzer is a framework that supports the general-purpose analysis of Travis build logs and provides dedicated Java and Ruby build analyzers that parse build logs in both languages and search for output traces of common testing frameworks.

The language-agnostic BuildAnalyzer reads-in a build log, splits it into the different build phases, and analyzes the build status and runtime of each phase. The fold for the script phase contains the actual build and continuous testing results. The BuildAnalyzer dispatches the automatically determined sub-BuildAnalyzer for further examination of the build phase.

For Java, we support the three popular build tools Maven, Gradle, and Ant. In Java, it is standard procedure to use JUnit as the test runner, even if the tests themselves employ other testing frameworks, such as PowerMock or Mockito. Moreover, we also support TestNG, the second most popular testing framework for Java. Running the tests of an otherwise unchanged project through Maven, Gradle and Ant leads to different, incompatible build logs, with Maven being the most verbose and Gradle the least. Hence, we need three different parsers to support the large ecosystem of popular Java build tools. As a consequence, the amount of information we can extract from a build log varies per build technology used. Moreover, some build tools give users the option to modify their console output, albeit rarely used in practice.

 T E S T S
Running nl.tudelft.watchdog.ClientVersionCheckerTest
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.04 sec

Results :

Tests run: 1, Failures: 0, Errors: 0, Skipped: 0

[INFO] All tests passed!

The listing above shows an excerpt of one test execution from the TestRoots/WatchDog project. In the output, we can see the executed test classes (line 4), and how many tests passed, failed, errored and were skipped. We also get the test execution time (line 5). Moreover, Maven prints an overall result summary (line 9) that the BuildAnalyzer uses to triage its prior findings. Line 11 shows the overall test execution result. Our BuildAnalyzer gathers all this information and creates, for each invoked project, a CSV table with all build and test results for each job built. We then aggregate this information with information from the build status analyzer step by joining their output. TravisTorrent provides easy access to this data.

The listing below shows the equivalent Gradle output. The silent Gradle becomes more verbose when a test fails, providing us with similar information to our first listing.


By contrast, in Ruby, the test framework is responsible for the console output: it is no different to invoke RSpec through Rake than through Bundler, the two predominant Ruby build (support) tools. For Ruby, we support the prevalent Test::Unit and all its off springs, like MiniTest. Moreover, we capture behavior driven tests via RSpec and Cucumber support.

Build Linearization and Mapping

If we want to answer questions such as ``how much latency does CI introduce,’’ we need to make a connection between the builds performed on Travis and the repository which contains the commits that triggered the build. We call this build linearization and commit mapping, as we need to interpret the builds on Travis as a directed graph and establish a child-parent relationship based on the Git commits that triggered their execution.

Commit Build Mapping

The above picture exemplifies a typical GitHub project that uses Travis for its CI. In the upper part (1), we see the Travis builds (§1-§9), which are either passed (§1-§6, §9), canceled (§7), or broken (§8). In the lower part, we see the corresponding GIT repository hosted on GitHub with its individual commits (#A-#H). Commits #D1-#D3 live in a pull request, and not on the master branch, traditionally the main development line in GIT. There are many complex scenarios that can occur:

  1. Build §1 showcases a standard situation, in which the build passed and the commit id stored with the build leads to the correct commit #A that triggered build §1. However, there are a number of more complex situations.

  2. If multiple commits are transferred in one git push (3), only the latest of those commits is built (§2). In order to get a precise representation of the changes that lead to this build result, we have to aggregate commits #B and #C.

  3. It is a central function of Travis CI to support branches or pull requests (4) such as commit #D1. When resolving builds to commits, we know from the API that §3 is a pull request build). Its associated commit points us to a virtual integration commit #V1 that is not part of the normal repository.

  4. In the case of build §6 on the same pull request (6), its direct predecessor is unclear: we traverse from #V3 to both 1) commit #D2 in the pull request, which is known, and to 2) #E on the master branch, which is unknown and cannot be reached from any of our previous commits #D2, #D1, or #C. This is because there was an intermediate commit #E on the master branch in-between, and pull requests are always to be integrated onto the head commit of the branch they are filed against. In such a case, one build can have multiple parents, and it is undecidable whether the changes in #D3, #E or a combination of both lead to the build result §6.

  5. Build §5 shows why a simple linearization of the build graph by its build number would fail: It would return §4 as its predecessor, when it really is §2 (7).

  6. Finally, when merging branches or pull requests (8), a similar situation to step 3. occurs, in which one merge commit #H naturally has two predecessors.