Prapr Save

Practical Program Repair via Bytecode Mutation

Project README

Maven Central

Source code of PraPR is now available at PraPR-SC.

PraPR: Practical Program Repair via Bytecode Mutation

Table of Contents


PraPR is a simplistic, yet effective, automatic program repair (APR) technique based on simple mutation operators. This repository is the official website for PraPR. This document, besides explaining how one can use PraPR, presents the main features of the tool.

We reiterate that PraPR, being a JVM bytecode-level APR, is able to fix JVM programming languages other than Java. Most of these languages (including Kotlin) are compatible with Maven, so our Maven plugin could be used for any Maven-based Kotlin project. However, since most of the times Kotlin developers tend to use Gradle as their build system, we have also included a Gradle plugin for PraPR which we are going to explain in this document.

PraPR Setup

PraPR can be used in two main forms: as a Maven plugin or as a Gradle plugin. In order to facilitate demonstration, we have also prepared a Docker image through which the users can try PraPR.

Maven Plugin

PraPR is available on Maven Central Repository in the form of a Maven plugin. You can obtain the plugin for PraPR by just configuring your target POM file.

In order to see how PraPR works, you will need a buggy program. We have prepared four of them for your convenience; they are located in the subdirectory examples. Before giving the instructions special to the example programs, let's see how we can configure a buggy program so that PraPR can fix it. We need to stress that the program, in order to be fixed by PraPR, has to have a test suite with at least one failing test case. Running PraPR with its default options is as simple as adding the following snippet in the POM file for the target program:


You can also customize PraPR's behavior by using the following template.

			<threads> <!-- NUMBER OF THREADS TO BE USED DURING MUTATION --> </threads>
                <!-- <mutator>ALL</mutator> ACTIVATES ALL THE AVAILABLE MUTATORS -->
                <!-- <mutator>PIT</mutator> ACTIVATES TRADITIONAL MUTATORS -->
                <!-- <mutator>PRAPR</mutator> ACTIVATES ALL THE MUTATORS SPECIFIC TO PRAPR -->
				<!-- <param>LOG</param> HUMAN READABLE RANKED LIST -->
                <!-- COULD BE "junit" (default), "testng", or "junit5" -->
            <!-- ET CETERA -->
        <!-- IN CASE YOU DECIDED TO USE JUNIT 5, AFTER SETTING THE VALUE OF testPlugin TO "junit5" -->
        <!-- <dependencies>
        </dependencies> -->

Once you configured the POM file (by filling the blanks as you wish), you can try the following command to run PraPR. This will automatically download PraPR plugin (and all of its dependencies), and begin fixing the program.

mvn org.mudebug:prapr-plugin:prapr

Please note that for the sake of maximizing compatibility of PraPR with the existing platforms, we choose to compile the tool using JDK 1.7. Thus, if you have got JDK 1.7+ on your machine, you will have no problem running PraPR using the above command. However, since Defects4J programs are not compatible with newer versions of JDK, you want to fix those programs using JDK 1.7. If you are using this for the first time, you might encounter a problem. This is because as of June 2018, Maven team (due to security reasons) have disabled the address for the central repository that once used to be the default address. You can easily work around this problem by using an additional switch in the command line when you invoke Maven.

mvn org.mudebug:prapr-plugin:prapr -Dhttps.protocols=TLSv1.2

There are also several command-line options that you might want to know; these include but not limited to:

  • -DverboseReport=false instructs PraPR to not to generate dump class files. This flag is, by default, true so that PraPR generates a subdirectory inside reports directory and dumps there all the class files corresponding to each plausible fix.
  • -DsuspStrategy determines the formula for computing suspiciousness values for mutations. Default value for this property is OCHIAI which means that PraPR, by default, uses Ochiai formula to assign suspiciousness values for mutations. You can also try other formulae such as TARANTULA. This is highly extensible, and the user can extend PraPR by adding more fault localization formulae.
  • -DreorderTestCases=false disables the heuristic reorder of test cases that is meant to maximize the chance of triggering of early exit during mutation testing.
  • -DmutateSuspStmt using this variable you can instruct PraPR to use a specific suspiciousness checker. The default value of this variable is DEFAULT which means that PraPR shall mutate the statements covered by all failing test cases. The value WEAK instructs PraPR to mutate an instruction only if it is covered by some failing tests, while NONE disables the suspiciousness checker altogether, hence PraPR mutates as many instructions as possible. Please note that for reasonably large programs, the configs WEAK and NONE might call for a large amount of heap space as the framework might generate a huge number of mutants. For Maven projects, you can use the variable MAVEN_OPTS to set the heap size prior to invoking PraPR.

Support for Multi-module Maven Projects

By default, for each sub-module within a multi-module project, PraPR (similar with PIT) repairs only the classes defined in the same module as the test suite. However, in practice, the tests within a sub-module may test source code defined within another sub-module. In that case, you can fire the following command from the root directory of the project to be repaired:

mvn org.mudebug:prapr-plugin:praprM

Note that a multi-module project may have a large number of modules, and you do not want to repair all of them (e.g., you only want to repair the ones with test failures). In this way, you can configure the following options to optimize your repair experience:

targetModules: running PraPR only on certain target modules (e.g., the modules with test failures). You can simply use it from the command line with -DtargetModules=firstModule,secondModule, or from the pom.xml:


excludedModules: filtering out certain modules (e.g., the modules without test failures) for PraPR. You can simply use it from the command line with -DexcludedModules=firstModule,secondModule, or from the pom.xml:


Gradle Plugin

In case that you want to use Gradle, we have prepared a plugin for Gradle through which you can run PraPR. You can find the JAR file for PraPR's Gradle plugin under the directory prapr-gradle-plugin in this repository. Once you download the file prapr-gradle-plugin-2.0.0.jar, you can put it in a directory that will be used as an alternative to Maven local repository. Let's assume that the file is downloaded inside a directory named my-gradle-repo. You can instruct Gradle to use this directory as a last resort when looking for the plugin for PraPR by using the following command in its appropriate place inside the build script, i.e. build.gradle.

repositories {
    flatDir { dir '/path/to/my-gradle-repo' }
    // et cetera

Once you set a mirror for the local repository, you can add the plugin into the classpath and invoke it. This is done through the following command.

dependencies {
    classpath 'org.mudebug.gradle.prapr:prapr-gradle-plugin:2.0.0'
    // et cetera

With that being set, you may apply and configure PraPR plugin as follows.

apply plugin: 'org.mudebug.prapr'

prapr {
    threads = /*number of threads*/
    outputFormats = [/*output formats, such as "HTML" and "LOG"*/]
    targetClasses = [/*target classes to be mutated*/]
    testPlugin = [/*test plugin which could be "junit" (which supports JUnit up to 4.6), "testng", or "junit5"*/]
    // et cetera

It is worth noting that you may omit either (or all) of the properties listed in prapr block. Once you omit, the Gradle plugin for PraPR uses default values for the omitted properties. The default value for threads is 1, while the default value for outputFormats is HTML, LOG, and COMPRESSED-XML, and that of targetClasses is groupId.* where groupId is the group ID for the project.

Please note that in order to be able use JUnit 5, you will need to refer to an external library. Fortunately, this library is readily available in Maven Central Repository. You can refer to JUnit 5 library through the following commands used at their appropriate place inside the build script.

dependencies {
    prapr 'org.pitest:pitest-junit5-plugin:0.4'
    // et cetera

After configuring the build file you can invoke PraPR by using the command gradle prapr-repair in the command-line at the root of the project.

Docker Image

The easiest way to try PraPR is to use our Docker image. We have shipped a pre-configured version of PraPR in the form of a Docker image ( Using this image the users will have access to PraPR and all the bugs that we have tested PraPR with.

In order to be able to use our Docker image, you need to have an instance of Docker installed on your computer. Please follow the installation instructions specific to your operating system, and install Docker on your computer.

Once you installed Docker, before trying the following commands, please make sure that it is running and is ready to be used.

sudo docker logout
sudo docker container run -it prapr/prapr

These commands (that are intended to be executed on a Linux terminal) will fetch PraPR image and run the container. Please note that the first command is necessary for newer versions of Docker. Note further that Mac OS or Windows users do not need to prefix the commands with sudo; they can simply use the following commands to get PraPR running.

docker logout
docker container run -it prapr/prapr

After downloading the image, the system will automatically begin executing the PraPR image, which is a pre-configured Ubuntu Linux. Once started, the system will automatically be redirected to /home/prapr/. We have provided the users with two commands using which they can fetch a Defect4J (or Defexts) bug, or invoke PraPR. The following command shall invoke PraPR wrapper and show all the bugs ids that this Docker image recognizes.

prapr-fix --all-bugs

Bug ids are in the form of subject-bug where subject is the subject project name (e.g. Chart, Time, etc.), and bug is the bug number. For example, Lang-10 identifies the bug Lang-10 from Defects4J (we stress that the wrapper script is case sensitive). Once we know the bug ids, we can invoke PraPR on the bug using the following command.

prapr-fix subject-bug

This command downloads the designated bug, before configuring and invoking PraPR on it. For example, prapr-fix Lang-10 downloads the bug Lang-10, and applies PraPR on it.

We can use the command checkout subject-bug to download the bug without invoking PraPR. All the downloaded bugs will be stored in the home directory of the container at /home/prapr.

Note: Except for Closure bugs (and a number of Math bugs), PraPR needs less than 16 GB of RAM. Some Closure bugs might need up to 64 GB of RAM.

Note: The Linux that we have shipped takes some space on your disk. Also downloading the bugs, and trying them, will quickly add up. So, please make sure that you have at least 50 GB of free space on your root drive (/ on Unix, and C: on Windows, systems).

PraPR Demonstration

We have prepared two real-world programs (one Java and one Kotlin) and two toy programs (one Java and one Kotlin). The real-world Kotlin program uses Gradle, while the rest use Maven. These examples demonstrate how PraPR is able to run under different build systems and applied on different JVM languages.

In order to get PraPR fix these programs, we recommend cloning this repository, and navigate into it, using the following commands in your command-line:

git clone
cd prapr

Fixing Lang-33 from Defects4J

Apache Commons Lang is a large, Maven-based Java project. Lang 33, is indeed Apache Commons Lang with bug Lang-#33 of Defects4J in it. The bug is located in line 910 of org/apache/commons/lang3/ This bug is a non-trivial, real-world bug, and could be fixed by doing the following replacement. We have to replace

classes[i] = array[i].getClass();


classes[i] = array[i] == null ? null : array[i].getClass();

You can use PraPR to fix the bug by executing the following commands (please note that Defects4J programs need JDK 1.7 to work).

cd examples
cd Defects4J
cd Lang-33
mvn clean test -DskipTests
mvn org.mudebug:prapr-plugin:prapr

After seeing the (green) BUILD SUCCESS message, you can examine the fix reports so that you can apply the appropriate plausible fix. The reports, as well as all the supporting information, will be placed under the directory {$project.base}/target/prapr-reports/*/, where * is a number representing the time and date at which the tool is ran. Under that directory you can find fix-report.log which is a human readable, ranked list of fixes. You might also want to use the visualized report by opening index.html in a web-browser. Please refer to the Secion Reporting for more information about fix reports. You can find dumped mutations under the subdirectory pool. With the help of the LOG file and a decompiler installed on your favorite IDE, you can see how patches can be applied in the source code.

Fixing jejin-984f7567 from Defexts

jejin is a large, real-world Gradle-based Kotlin program that contains more than 9700 lines of code all in Kotlin. The bug jejin-984f7567 is fixable by replacing

this::class.declaredMemberProperties.forEach {


this::class.memberProperties.forEach {

at line 22 of jenjin-core/src/main/kotlin/com/binarymonks/jj/core/components/Component.kt which is located inside the subproject jejin-core. This suggests that bug is located inside the subproject jejin-core and other subprojects do not need to be fixed. We could gain the same information by compiling the project and running test cases. We would realize that only test cases of the subproject jejin-core fail. This suggests that we don't need to waste resources by running PraPR on other subprojects of this huge project, and we can fix the bug just by applying the plugin on the subproject that actually contains the bug. We have already done this for you and you can read the build script and grasp the details.

In order to fix this program using the following commands (please note that jejin requires JDK 1.8 and Gradle 4.9 to work)

cd examples
cd Defexts
cd jenjin-984f7567c83df2778b3d7887380839b757008340
gradle clean build -x test
gradle prapr-repair

After seeing the (green) BUILD SUCCESSFUL message, you can go ahead and get the LOG file from the build directory located at {$project.base}/jejin-core/build/reports/prapr-report/*/fix-report.log. As you can see, the LOG report is placed inside the build directory of the suproject jejin-core.

Fixing Toy Programs

There is a small Java, and also a small Kotlin, program inside examples directory. We thought some reviewers might find smaller programs with seeded bugs useful for demonstration and comprehension. The Java program is located at examples/toy-java-program/, while the Kotlin program is located at examples/toy-kotlin-program/. The bug for the Java program is located in line 22 of com/example/, and the bug for the Kotlin program is located in line 18 of hello/KotlinHello.kt. One can follow the same instructions for fixing Lang-33 and jejin-984f75 to fix these programs.

PraPR Reports

PraPR is able to produce two kinds of human readable fix reports. The file fix-report.log is a ranked list of fixes. The ranking scheme employed by PraPR is described in the paper. This file also provides the total number of plausible fixes, as well as patches, that are generated. Last but not least, LOG files specify the name of the dump file for each mutant which is a plausible fix, so that the user can refer to pool of dumped mutants so as to retrieve the dump file and examine its contents in an IDE. In this way, the user can clearly understand how a patch looks like when it is applied on the source code.

PraPR also produces a visualized HTML report, so that the users can actually see the place and description of fixes in the context of subject program source code. Please note that the report contains only suspicious code elements, so that the user will not get lost in a huge HTML page.

Here are two screenshots from the gerenated HTML files. The lines that are covered are highlighed using pale green color, while lines with a killed mutation applied on them are highlighted with pink, and plausible fixes are highlighted with a darker green.


The user can hover the mouse pointer over the line number and see the details of mutations applied at that line.


PraPR also visualizes the number of plausible fixes, as well as all patches. For larger projects this will help the users a lot in locating the place of a plausible fix (they do not need to look into classes/packages that do not have any plausible fixes). The following screenshot illustrates an example.


Finally, PraPR has inherited the capability of producing XML reports from PIT. XML reports are meant to be processed by machine. Since XML report can grow very large for programs like Closure, PraPR compresses the XML files that it produces. The XML contents are compressed using gzip format.

Dumped Mutants

For each plausible fix, PraPR dumps the resulting mutant inside the subdirectory pool under the directory prapr-reports/*/. From the LOG file generated by PraPR, one will know which dump file corresponds to which plausible fix. Dump files are essentially .class files corresponding to the mutated class that contains the plausible patch. The user can take advantage of a Java bytecode decompiler to decompile the resulting class file. Eclipse Class Decompiler is a sophisticated decompiler that is able to retrieve the original line numbers and align the line numbers in the mutated code with that of the original source code.

Eclipse Class Decompiler is freely available as an Eclipse plugin. Below you can see a screenshot from the decompiled mutant corresponding to the genuine patch for the toy Java example.

Mutant for the genuine fix:


Configuring Eclipse Class Decompiler

We are in the process of integrating a class decompiler into PraPR, for better user experience. For the time being, however, we are taking advantage of an Eclipse plugin for showing the patches inside the target program. We thought it might be a little bit confusing for some users to work with Eclipse Class Decompiler, so we are going to give the instructions on configuring the plugin. Installation directions, as well as how to configure default file association, is already given in the official website of the plugin.

After installing the plugin, you will need to open the window "Preferences" from "Window -> Preferences." In that window, under the item "Java," select the item "Decompiler." Then select the appropriate decompiler library from the drop-down list "Default Class Decompiler." We recommend "FernFlower" which supports JDK 1.8. After selecting the library, you will need to check both items "Output original line numbers as comments," and "Align code for debugging."

Finally, you should select the item "Disassember" under the item "Decompiler," and check the item "Show source line numbers."

PraPR Patches

We have prepared a set of patch files based on the diff between the decompiled mutants corresponding to each plausible patch that we believe they are genuine fixes (almost all of them are syntactically the same as the programmer-written patches and reasoning about those patches that are not syntactically the same is quite easy). These patches are located under the subdirectory patches of this repository. Please note that programmer-written patches are already shipped with Defects4J and Defexts and reviewers can refer to those.

System Requirements

  • OS: Ubuntu Linux or Mac OS X.
  • Build System: Maven 3.2+ or Gradle 4.8+.
  • JDK: Oracle Java SE Development Kit 7u80 (recommended for Defects4J) and 8u171 (recommended for Defexts).
  • IDE: Eclipse Oxygen.


PraPR is a research project and part of Ali Ghanbari's Ph.D. thesis at The University of Texas at Dallas. The paper that introduces the idea of PraPR, and reports the results of an extensive empirical study on state-of-the-art APR techniques, is published in the proceedings of 28th ACM SIGSOFT International Symposium on Software Testing and Analysis (ISSTA 2019). Please use the following BibTeX snippet in case you wish to cite our work.

 author = {Ghanbari, Ali and Benton, Samuel and Zhang, Lingming},
 title = {Practical Program Repair via Bytecode Mutation},
 booktitle = {Proceedings of the 28th ACM SIGSOFT International Symposium on Software Testing and Analysis},
 series = {ISSTA 2019},
 year = {2019},
 isbn = {978-1-4503-6224-5},
 location = {Beijing, China},
 pages = {19--30},
 numpages = {12},
 url = {},
 doi = {10.1145/3293882.3330559},
 acmid = {3330559},
 publisher = {ACM},
 address = {New York, NY, USA},
 keywords = {Fault localization, JVM bytecode, Mutation testing, Program repair},

You can obtain a copy of the paper through the link FULL-PDF.

Our Demo paper has just been accepted for publication in ASE 2019 Demonstrations section. The paper presents a high-level overview of engineering of PraPR. Please use the following BibTeX snippet in case you wish to cite our work.

 author = {Ghanbari, Ali and Zhang, Lingming},
 title = {PraPR: Practical Program Repair via Bytecode Mutation},
 booktitle = {Proceedings of the 34th IEEE/ACM International Conference on Automated Software Engineering},
 series = {ASE 2019},
 year = {2019},
 note = {to appear}

You can obtain a copy of the paper through the link DEMO-PDF.

In another short paper, I have described our long-term goals in automated program repair. The paper is accepted for publication in ASE 2019 SRC section. Please use the following BibTeX snippet in case you wish to cite our work.

 author = {Ghanbari, Ali},
 title = {Torward Practical Automatic Program Rerpair},
 booktitle = {Proceedings of the 34th IEEE/ACM International Conference on Automated Software Engineering},
 series = {ASE 2019},
 year = {2019},
 note = {to appear}

You can obtain a pre-print of the paper through the link SRC-PDF.

PraPR on YouTube

As part of the artifact evaluation process for our ISSTA'19 paper, we have released a YouTube video demonstraing how to use the Docker image for PraPR.

Open Source Agenda is not affiliated with "Prapr" Project. README Source: prapr/prapr
Open Issues
Last Commit
3 months ago

Open Source Agenda Badge

Open Source Agenda Rating