sbt-coursera / sbt-coursera   0.7

BSD 3-clause "New" or "Revised" License GitHub

SBT plugin for automatic grading of assignments in Coursera.

Scala versions: 2.10
sbt plugins: 0.13

Sbt Plugin for Automatic Grading of Assignments on Coursera

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This is an SBT plugin for creating Scala and Java projects that can be automatically graded on Corusera. The plugin is meant to be used with the set of scripts for managing the cluster infrastructure.


To use the sbt-coursera plugin you need to do two things:

  • Add the plugins.sbt file with the following contents to the <base-dir>/project folder. The file should contain the following:

    addSbtPlugin("ch.epfl.lamp" % "sbt-coursera" % "0.3")
  • Add your custom build file to the <base-dir>/project by filling in the template file.


The build can be reused for different project handouts, it abstracts over all project specific settings. This is done in the projectDetailsMap defined in the main build.sbt file.

The elements in the projectDetailsMap are mostly self-explanatory. The packageName field is used in two places during the build process

  • To select the source files that are handed out to students, see the handoutFiles in your scala build file that extends.
  • To select which tests are compiled and executed when testing a submission, see selectTestsForProject in ProgFunBuild.scala and runScalaTest in ScalaTestRunner.scala

Main Project

The main project (named assignment) is used by the students to compile, run and test their code. It's also used by the TAs to write assignments, write private and public test.

It is a standard SBT project, main soruces in src/main/scala, tests src/test/scala. Use tasks such as compile, test or eclipse as usual. The project additionally defines the submit task which allows the students to upload their solution to the coursera servers.

Finally, the project defines a createHandout task which will create a .zip file with all the files that we hand out to the students. The content of this .zip file is defined in the handoutFiles setting of the main build.sbt file. To prevent unwanted jars in the .zip file one needs to do a clean, set currentProject := "<project-name>", eclipse, and then run the createHandout` command.

Grading Project

We define a second sbt project (named submission with project root is directory submission) that is used to grade an assignment that has been submitted to coursera. First of all, it decodes the student's source code from the json file (downloaded by the gradingImpl script) and unpacks it in the directory submission/src/main/scala. Note that the test sources are picked up from the main project, i.e. src/test/scala (which contains all private tests if we are in the solutions branch).

In order to grade an assignment, one has to run the submission/grade task. But before, one has to define the project that's being graded, so that the correct tests are executed. This has to be done using the set command:

set (partIdOfGradingProject in submissionProject) := "idString"

where partIdOfGradingProject is one of the assignment part ids used in the projectDetailsMap of the main build.sbt file. Defining the partIdOfGradingProject setting can also be done when running from the command line:

sbt `(partIdOfGradingProject in submissionProject) := "idString"` submission/grade

The submission/grade task will then unpack the source, compile it, compile the tests, run the tests, run the stylechecker, and upload the generated feedback via the coursera API.


In Settings.scala there's a boolean offlineMode which is useful when coding on the build definition. If it is set to true, the build will

  • not decode the json file and extract the source code
  • not clean the sources in the submission project
  • not upload feedback

Creating handouts

In sbt in the master branch, do the following (replace NAME_OF_THE_PROJECT with the actual project name):

> createHandout NAME_OF_THE_PROJECT

Grab the generated zip file from the target folder.

Working on one specific assignment

When working on one specific assignment, you'd like to avoid the sources and tests of other assignments from being compiled / tested. This can be achieved using the setting currentProject in the main build.sbt file.

If currentProject == "", then all sources are compiled and all tests are executed.

Test Weights and Sandboxing

A public test suite (for students) should extend org.scalatest.FunSuite and use the "test" method defined there. In order to add test weights and test execution sandboxing, the private test suites mix in the trait grading.GradingSuite which is defined in the solutions branch. This triat overrides the "test" method to sandbox the executed code and adds an additional weight argument allowing to define the grade weight of each test.

The entire source code for all the assignments is kept in this repository. The sources for each assignment have to be in a separate package (project1, ...).

The createHandout task (available in master) will only include the tests and sources of the specific project for which a handout archive is generated. Similarly, the submission/grade task will only compile and execute the tests of the project being tested.

NOTE: after adding the grading.GradingSuite trait to a test suite (as in the solutions branch), it can no longer be executed in eclipse using the eclipse JUint runner.

Running weighted tests and Scalastyle

When working on an assignment, you can use the sbt task styleCheck to run Scalastyle on the source files.

To run the test suite with test weights (only works in branch solutions) while working on an assignment, you can use the scalaTest task. In order to run the tests without computing a score, use the ordinary test task (in both branches).

NOTE: all of these tasks tasks take the currentProject setting into account, see above.


Students will never have to touch any build files.

The main build.sbt file defines settings for all projects.

The file submission/settings.sbt contains settings only needed for grading. This file contains a secret API key and should not be distributed to the students.