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Gradle-based Java AutoGrader
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README.md

Maven Central Build Status ktlint

RiceChecks

Current status: early alpha. Please email dwallach@rice.edu before trying to use this.


This project contains an autograder for Java and Gradle-based student projects. We try to simplify the process of specifying how unit tests and such are mapped to points, leveraging Java annotations, so your grading policy is embedded in your code. It's like JavaDoc, but for grading policies.

The output looks something like this for a successful project:

┌─────────────────────────────────────────────────────────────────────────────
│ Autograder for Sorting                                                      
│ Implement Many Sorting Algorithms                                           
├─────────────────────────────────────────────────────────────────────────────
│
│ HeapSort: 2 of 2 tests passed                                    2.0/2.0 ✅
│
│ InsertionSort: 2 of 2 tests passed                               2.0/2.0 ✅
│
│ PatienceSort: 2 of 2 tests passed                                2.0/2.0 ✅
│
│ ShellSort: 2 of 2 tests passed                                   2.0/2.0 ✅
│
│ No warning / style deductions                                    1.0/1.0 ✅
│
│ Test coverage meets 90% (by line) requirement                    1.0/1.0 ✅
│ - Coverage of edu.rice.sort.HeapSort: 100.0% (31/31)             
│ - Coverage of edu.rice.sort.InsertionSort: 100.0% (9/9)          
│ - Coverage of edu.rice.sort.PatienceSort: 100.0% (20/20)         
│ - Coverage of edu.rice.sort.PatienceSort.Pile: 100.0% (1/1)      
│ - Coverage of edu.rice.sort.ShellSort: 100.0% (14/14)            
│
├─────────────────────────────────────────────────────────────────────────────
│ Total points:                                                  10.0/10.0 ✅
└─────────────────────────────────────────────────────────────────────────────

Whereas, for a project with some bugs, you might see:

┌─────────────────────────────────────────────────────────────────────────────
│ Autograder for RPN                                                          
│ Simple RPN Calculator                                                       
├─────────────────────────────────────────────────────────────────────────────
│
│ Correctness: 0 of 2 tests passed                                 0.0/6.0 ❌
│ - edu.rice.rpn.RpnCalcTest.testBasicArithmetic: failed             (-3.0)
│ - edu.rice.rpn.RpnCalcTest.testStackHandling: failed               (-3.0)
│
│ Warning / style deductions                                       0.0/1.0 ❌
│ - CheckStyle (main): 0 of 1 files passed                         
│ - GoogleJavaFormat: 1 of 2 files passed                          
│   run the gradle <googleJavaFormat> task to fix
│
│ Classes with coverage below 90% (by line) requirement            0.0/3.0 ❌
│ - Coverage of edu.rice.rpn.RpnCalc: 73.8% (31/42)                
│   (including one anonymous inner class)
│ - See the coverage report for details:                           
│   ./build/reports/jacoco/index.html
│
├─────────────────────────────────────────────────────────────────────────────
│ Total points:                                                   0.0/10.0 ❌
└─────────────────────────────────────────────────────────────────────────────

Table of contents

Concepts

The essential design of the autograder is:

  • You decorate your unit tests with annotations that specify their associated projects and points values.
    • If you've got a single master repository for multiple separate projects, you do these annotations once and they stay put in your master branch. They have no impact on student code.
  • You extract a grading policy for every given project, which you then include in the config directory that is handed out to your students.
    • This policy is a human-readable YAML file, so you can easily review it, for example, to ensure that you have the expected total number of points.
  • You provide your students with a build.gradle file, specifying all the tasks that need to be run. This includes JUnit5 tests (@Test and @TestFactory), CheckStyle, google-java-format, ErrorProne, and JaCoCo.
  • You add our provided autograder code to build.gradle, which runs all these gradle tasks, writing log files to the build directory. We change the default configuration so as many tasks will complete as possible, rather than stopping immediately when a task fails.
  • The autograder runs as a standalone Java program, reading all the build output logs and evaluating them with respect to the grading policy. Results are printed to standard output, and then the autograder either exits with 0 or non-zero, which is then understood by CI services to imply success or failure.
  • You configure your CI service to run all of this every time there's a push to your Git server. (For example, you might provide a .travis.yml file to arrange for Travis-CI to run the autograder on GitHub commits.)
  • Exactly the same autograder run on the CI server as run locally on the students' computers. This means that students can rapidly see the autograder results, locally, and further benefit from the CI service's version to ensure they didn't forget to commit or push a file.
  • Human graders can look at the CI output as well, transcribing this into the university's learning management system (e.g., Canvas), while also looking over the student projects for anything sketchy.
  • We provide you several example projects so you can see how this all fits together.

RiceChecks, itself, is written in Kotlin, and should be able to process student projects written in Java, Kotlin or any other JVM language, although our focus is on Java-based student projects, at least for now.

RiceChecks, itself, is compiled with OpenJDK 8 and tested with both OpenJDK 8 and OpenJDK 11. It's unlikely to work on earlier JDK releases.

Annotations

RiceChecks supports the following annotations:

  • You specify one @GradeProject annotation per project. This annotation can appear on any Java class, or it can appear on a package (i.e., inside a package-info.java file). For example, for a project on implementing sorting algorithms you might write:
/* src/main/java/edu/rice/sort/package-info.java */
@GradeProject(
    name = "Sorting",
    description = "Implement Many Sorting Algorithms",
    warningPoints = 1.0,
    coveragePoints = 1.0,
    coveragePercentage = 90)
package edu.rice.sort;
  • The warningPoints are granted if all of the following checks come up clean:

  • The coveragePoints and coveragePercentage are part of the coverage policy, detailed below.

  • You then need one or more GradeTopic annotations:

@GradeTopic(project = "Sorting", topic = "HeapSort")
public class HeapSortTest { /* ... */ }
@GradeTopic(project = "Sorting", topic = "InsertionSort")
public class InsertionSortTest { /* ... */ }
  • @GradeTopic annotations can appear on any Java class or package. They allow you to create groupings of individual unit tests. You can specify an optional maxPoints = N attribute. If the individual unit tests associated with the topic add up to more than the given maxPoints, then those deductions will be capped at the given maximum number. If unspecified, the maximum number of points is computed based on all the unit tests associated with the topic.

  • You then annotate each unit test with a Grade annotation:

public class InsersionSortTest {
    @Test
    @Grade(project = "Sorting", topic = "InsertionSort", points = 1.0)
    public void insertionSortStrings() { /* ... */ }
}
  • For JUnit5 test factories, which return a list of tests, whose length isn't known until runtime, you specify the number of points per test, and the maximum number of points for the whole list of tests:
public class InsersionSortTest {
    @TestFactory
    @Grade(project = "Sorting", topic = "InsertionSort", points = 1, maxPoints = 5)
    List<DynamicTest> testIntegers() { /* ... */ }
}

Annotation debugging and extraction

The process of writing down all these annotations can be tedious, and it's easy to make mistakes. Once you think you're ready, run the autograderDebugAnnotations gradle task, and something like this will appear on the console:

name: "RPN"
description: "Simple RPN Calculator"
maxPoints: 10.0
warningPoints: 1.0
useCheckStyle: true
useGoogleJavaFormat: true
useJavacWarnings: true
coveragePoints: 3.0
coverageStyle: "LINES"
coveragePercentage: 90.0
coverageAnnotations:
- scope: "CLASS"
  excluded: false
  name: "edu.rice.rpn.RpnCalc"
topics:
- name: "Correctness"
  maxPoints: 6.0
  tests:
  - points: 3.0
    maxPoints: 0.0
    className: "edu.rice.rpn.RpnCalcTest"
    methodName: "testBasicArithmetic"
    testFactory: false
  - points: 3.0
    maxPoints: 0.0
    className: "edu.rice.rpn.RpnCalcTest"
    methodName: "testStackHandling"
    testFactory: false

Read it over and verify that what you see is consistent with what you expected. For example, make sure that the maxPoints attribute at the top is what you intended. Once everything is good, run the autograderWriteConfig task, which will place this same YAML contents into config/grade.yml, which you would then distribute as part of the project to your students.

You might also delete the autograderDebugAnnotations and autograderWriteConfig tasks from the build.gradle file before distributing it to the students to ensure they don't run those tasks by accident. If you want, you could even delete all the RiceChecks annotations (@Grade, etc.), although there's no harm in leaving them in.

Coverage testing

RiceChecks uses JaCoCo, which has a wide variety of ways that you can configure its Gradle plugin to either fail or pass the build based on different coverage policies. When we tried to just use this as-is, students were unhappy with the feedback. The way we specify and report coverage in RiceChecks is:

  • The top-level coverage policy appears in the GradeProject annotation.

    • With coveragePoints = N you specify the number of grade points (awarded all or nothing) for satisfying the coverage policy.
    • You specify a coveragePercentage you wish to require of every covered class.
    • You may optionally specify a coverageStyle; your choices are LINES or INSTRUCTIONS, corresponding to the same terms as JaCoCo understands them. If you're concerned that students might try to mash too much code onto a single line in order to game line-counting coverage, you might prefer the INSTRUCTIONS mode, which is based on Java bytecode operations, or you could require google-java-format, described above, which forces code to be formatted in a more reasonable fashion.
  • You annotate Java classes or packages (via package-info.java) with an @GradeCoverage annotation to note which project(s) care about coverage for those Java classes or packages.

@GradeCoverage(project = "Sorting")
public class HeapSort { /* ... */ }
  • You can set an exclude = true flag on the GradeCoverage annotation if you want to say that a particular class is not to be considered for coverage testing. This might make sense if you've enabled coverage testing on an entire package but wish to exclude a specific Java class within the package for coverage testing. A GradeCoverage annotation applies recursively to inner classes as well. If there are multiple applicable coverage annotations external to a class, the closest one wins.

  • Each class (or inner class) is evaluated for its coverage, for the desired metric, independently. Every class must pass for RiceChecks to award the coverage points.

  • What about lambdas or methods? JaCoCo measures per-method coverage, treating every lambda as if it's a separate method within the same class. RiceChecks only looks at the per-class summary data, which wraps up all methods and lambdas within that class.

  • For any inner class, once we've determined that it's subject to coverage testing, it will be measured for hitting the desired coverage level on its own, without any dependencies on its outer or further-inner classes.

  • For anonymous inner classes, contained inside a class that's subject to coverage, we accumulate the statistics from the anonymous inner class with its containing class, enforcing coverage requirements on their statistics' sums. (Since anonymous inner classes don't have names, this helps us avoid giving unhelpful feedback to a student.)

Sample projects

There are three sample projects, showing you how the RiceChecks autograder works. They are:

  • exampleRegex: students are asked to implement several regular expressions; their work is tested using JUnit5's TestFactory, which has a list of examples for each regex that should be accepted and another list of examples that should be rejected by the regex.
  • exampleRpn: students are asked to implement a simple RPN calculator; there are many cases, so we require minimum test coverage.
  • exampleSort: students are asked to implement four sorting algorithms; their work is tested with QuickTheories, generating hundreds of random inputs.

All of the code for these examples is borrowed from RosettaCode, to which we added our own unit tests and made other small changes. The code, as you view it in this repository, passes all tests and gets a perfect grade. You might try modifying one or more of the examples, introducing bugs, to see how the autograder responds.

Student project integration

The "example" projects have their build.gradle files configured to compile and use RiceChecks from the adjacent sources. When configuring a student repository for use with RiceChecks, you should start with standaloneSort/build.gradle, which has the following features:

  • Loads edu.rice.ricechecks:ricechecks-annotations:0.7.3 (just the Java annotations) as a regular dependency for student code.

  • Loads edu.rice.ricechecks:ricechecks:0.7.3 (the autograder tool) as part of a separate Gradle "configuration", ensuring that symbols from the tool don't accidentally autocomplete in students' IDEs.

Provides three Gradle tasks that invoke the autograder tool:

  • autograderDebugAnnotations -- this allows you to see the result of processing your annotations. You might verify, for example, that you had the desired number of total points. You might use this for yourself but delete the task from build.gradle before shipping your repo to the students.
  • autograderWriteConfig -- when you're happy with your annotations, this writes a YAML file to the config directory which is used by the main grading task later on. As with autograderDebugAnnotations, you might choose not to ship this to your students.
  • autograder -- this runs everything -- compiling the code, running the unit tests, and collecting all the coverage results -- and prints a summary to the console.

Ultimately, the autograder task replaces what might normally be a call to gradlew check in places like a Travis-CI .travis.yml file or a GitHub Actions workflow file.

Try it!

We took our three sample projects and created standalone repositories, which you might then clone and experiment with.

FAQs

  • Are there other Gradle-based Java autograders?

    And see also:

  • Why Gradle? The short answer: because it's popular and widely supported. Among other things, Gradle is widely used for Android applications. Whenever somebody comes out with a clever Java-related tool, they generally release a Gradle plugin for it. Students don't have to learn or understand Gradle to use RiceChecks. IntelliJ provides a "Gradle" tab on which students can click on the tasks they wish to run, including the autograder task provided by RiceChecks.

  • Can you build a Gradle plugin so I don't need all this custom code in the build.gradle file? You're welcome to have a go at it and submit a PR. I'm concerned about how to write such a thing in a general-purpose way, given all the different ways that different projects will configure Gradle. RiceChecks, by running as a completely separate Java process, avoids getting too entangled with Gradle, beyond knowing how all its log files are written. Curiously, as we've been using RiceChecks in our class, we've found and fixed a bunch of minor issues in the build.gradle file, while not needing to change the autograder itself.

  • Does RiceChecks work with {JUnit4, TestNG, ...}? Maybe? What really matters is how Gradle's test unit runner writes an XML log of its results into the build directory. If you use some other mechanism for running tests, then you'll need to extend the logic in JUnitScanner.kt.

  • RiceChecks only really supports JUnit5's @Test and @TestFactory. What will it take to more broadly support other JUnit5 test annotations? Most custom JUnit5 annotations that say "here's a test" could potentially be something we can treat as equivalent to either @Test or @TestFactory. RiceChecks hasn't yet been tested with some of the fancier JUnit5 features like multiple dynamicTest instances inside of a dynamicContainer. To support meta annotations or custom annotations from a project like Karate, RiceChecks would probably need its own meta annotation facility to tell it what to do. If there's a custom test runner involved, things will get more complicated.

  • What if I want to use something other than the assert statements built into JUnit5? RiceChecks only cares about whether a test method succeeds or fails. Hamcrest matchers or other such systems should work just fine. In our class, we sometimes use QuickTheories, which also has its own internal assertions. Gradle knows how to run the tests and it all looks the same when RiceChecks reads the logs.

  • What about Spotless or SpotBugs? Spotless is analogous to CheckStyle and google-java-format. SpotBugs is analogous to ErrorProne. You could certainly engineer support for additional tooling into RiceChecks, but it's not here right now.

  • Why are you using both CheckStyle and google-java-format? The nice thing about google-java-format is that it provides an auto-indenter that students can run as a Gradle task (googleJavaFormat). We still need CheckStyle to enforce other useful Java practices, like capital names for classes with matching filenames. CheckStyle saves us from weird scenarios where a Java program compiles on a case-insensitive filesystem (Windows or Mac) but not on a case-sensitive filesystem (Linux). Where CheckStyle and google-java-format had overlapping rules, we disabled the CheckStyle rule, since google-java-format generally knows how to automatically fix many of the rules that it wants to enforce.

  • Why do you write out the grading policy to a YAML file? Why not just re-read the annotations every time? Let's say you want to have "secret" unit tests that you don't initially give to your students, perhaps because you want to make them write their own tests before seeing yours. You can construct a policy with your tests present, save it to the YAML file, and then delete your "secret" Java test file prior to distributing the project to your students. When the student runs the autograder, it will notice that the "secret" tests are missing and treat them as having failed. When you later add them back in, everything works.

    Of course, we still rely on human graders to notice if a student edited the YAML file, or for that matter, edited the unit tests we provided to them.

  • How do you add "secret" test files into student projects after an assignment is live? We hand out our weekly projects on Monday morning with student unit tests due Thursday evening. On Friday morning, we pull every student repository, add the "secret" tests, commit, and push. Students will then have the benefit of both their tests as well as ours to make sure they get their submission solid before the Sunday evening deadline. If you prefer your students not to see your "secret" tests prior to the deadline, you could always do a similar process after the final submission deadline. The student would be able to see the tests, but it would be too late for them to change their code.

  • Why did you write the autograder itself in Kotlin? An important motivating factor was being able to easily leverage the efforts of other projects that do useful work for us. In particular, the ClassGraph project makes straightforward to extract annotations from Java code, and Jackson, has simple support for reading and writing XML, YAML, JSON, and a variety of other common formats. Since both ClassGraph and Jackson are just Java libraries, we could call them from Java, Kotlin, Scala, or any other JVM language.

    Since students will never need to see or understand the code for the autograder, we can use any JVM language, so we chose Kotlin. Kotlin gives an entirely pleasant experience for building a tool like RiceChecks. We also take advantage of the Arrow functional programming library.

  • Java8 versus Java11 versus... We want to support student projects written in Java8 or Java11, and eventually newer versions of Java as well. To that end, we compile RiceChecks using OpenJDK 8 and test it with both OpenJDK 8 (the examples within this repository) and OpenJDK 11 (the standalone demonstrations linked from the Try it! section).

    To support Java 11, you'll notice several minor differences in those examples' build.gradle files, but RiceChecks runs exactly the same.

    Migrating RiceChecks to newer versions of Java is unlikely to cause any problems. Migrating RiceChecks to newer versions of Gradle, on the other hand, is likely to be tricky. Certainly, the build.gradle file will need to evolve, and RiceChecks knows a lot about the XML files written out by Gradle as it runs a build. If those changed, RiceChecks would need additional updates.

  • Which Java distribution are you using? Amazon Corretto supports OpenJDK 8 and 11, providing up-to-the-minute bug fixes, and is used by Amazon for their own production services. Amazon also provides pkg files for Apple and msi files for Windows, allowing students to double-click and install. For Travis-CI, we just specify openjdk8 or openjdk11 and whatever they use seems to work just fine. For GitHub Actions, we just specify Java 1.8 or 11 and that seems to work as well.

  • Can I have machine-readable output from RiceChecks / Can RiceChecks send grades automatically to my server? After the autograder runs, it creates two files: build/autograder/report.json and build/autograder/report.yml (same data, your choice of serialization format). The information is a superset of the pretty-printed output, which tries to only print what the user really needs (e.g., only printing the names of failed unit tests, rather than the names of every unit test).

    After the autograder has finished running, your own code can pick up the autograder report and take further actions, like uploading it to a server. Keep in mind that students control their repositories, which includes the possibility of generating deliberately incorrect reports.

  • How can I do coverage testing on a per-method basis rather than per-class? You could extend the relevant code in JacocoScanner.kt, which is already getting a bit complicated, to enforce more complicated coverage policies. You'd also have to reconfigure the annotation system to allow @GradeCoverage annotations on methods, and you'd need to figure out what to do about lambdas and anonymous inner classes.

  • On Windows, when I run the autograder, I see a bunch of ?????'s rather than the nice Unicode borders around the autograder output. How do I fix that?

    • For IntelliJ, you can go to HelpEdit Custom VM Options... and add the line -Dfile.encoding=UTF-8. Restart IntelliJ and the Unicode should all work properly.

    • For Windows console users, check out Microsoft's new Windows Terminal. It's free and it seems to have lots of promising features.

    • For Mac users, the regular Terminal program, installed on every Mac, seems to do the right thing out of the box.

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