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A Database of Real Faults and an Experimental Infrastructure to Enable Controlled Experiments in Software Engineering Research
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Defects4J -- version 1.5.0 Build Status

Defects4J is a collection of reproducible bugs and a supporting infrastructure with the goal of advancing software engineering research.

Contents of Defects4J

The projects

Defects4J contains 438 bugs from the following open-source projects:

Identifier Project name Number of bugs
Chart JFreeChart 26
Closure Closure compiler 176
Lang Apache commons-lang 65
Math Apache commons-math 106
Mockito Mockito 38
Time Joda-Time 27

The bugs

Each bug has the following properties:

  • Issue filed in the corresponding issue tracker, and issue tracker identifier mentioned in the fixing commit message.
  • Fixed in a single commit.
  • Minimized: the Defects4J maintainers manually pruned out irrelevant changes in the commit (e.g., refactorings or feature additions).
  • Fixed by modifying the source code (as opposed to configuration files, documentation, or test files).
  • A triggering test exists that failed before the fix and passes after the fix -- the test failure is not random or dependent on test execution order.

The (b)uggy and (f)ixed program revisions are labelled with <id>b and <id>f, respectively (<id> is an integer).

Looking for additional bugs?

A number of additional bugs are available in "work-in-progress" status. These bugs meet the same properties as the ones above, but have only been minimized by one of the maintainers. Metadata and patch content can potentially change before these bugs are migrated into the master repository. These bugs may be used in experiments, but should not be considered as "stable" as the bugs in the master repository. If you use these bugs, please ackowledge their "beta status" in any publications.

Branch commons-compress-collections:

Identifier Project name Number of bugs
Collections Apache commons-collections 28
Compress Apache commons-compress 47

Branch additional-projects-4:

Identifier Project name Number of bugs
Cli Apache commons-cli 40
Codec Apache commons-codec 18
Csv Apache commons-csv 16
Gson Google Gson 18
JacksonCore Jackson JSON parser 26
JacksonDatabind Jackson data bindings 112
JacksonXml Jackson XML extension 6
JxPath Apache commons-jxpath 22
Jsoup jsoup HTML Parser 93

Setting up Defects4J


  • Java 1.7
  • Git >= 1.9
  • SVN >= 1.8
  • Perl >= 5.0.10

Java version

All bugs have been reproduced and triggering tests verified, using the latest version of Java 1.7. Note that using Java 1.8+ might result in unexpected failing tests on a fixed program version. The next major release of Defects4J will be compatible with Java 8.

Perl dependencies

All required Perl modules are listed in cpanfile. On many Unix platforms, these required Perl modules are installed by default. If this is not the case, you can use cpan (or a cpan wrapper) to install them. For example, if you have cpanm installed, you can automatically install all modules by running: cpanm --installdeps .


Defects4J generates and executes tests in the timezone America/Los_Angeles. If you are using the bugs outside of the Defects4J framework, set the TZ environment variable to America/Los_Angeles and export it.

Steps to set up Defects4J

  1. Clone Defects4J:

    • git clone
  2. Initialize Defects4J (download the project repositories and external libraries, which are not included in the git repository for size purposes and to avoid redundancies):

    • cd defects4j
    • ./
  3. Add Defects4J's executables to your PATH:

    • export PATH=$PATH:"path2defects4j"/framework/bin
  4. Check installation:

    • defects4j info -p Lang

Using Defects4J

Example commands

  1. Get information for a specific project (commons lang):

    • defects4j info -p Lang
  2. Get information for a specific bug (commons lang, bug 1):

    • defects4j info -p Lang -b 1
  3. Checkout a buggy source code version (commons lang, bug 1, buggy version):

    • defects4j checkout -p Lang -v 1b -w /tmp/lang_1_buggy
  4. Change to the working directory, compile sources and tests, and run tests:

    • cd /tmp/lang_1_buggy
    • defects4j compile
    • defects4j test
  5. The scripts in framework/test/ are examples of how to use Defects4J, which you might find useful as inspiration when you are writing your own scripts that use Defects4J.

Command-line interface: defects4j command

Use framework/bin/defects4j to execute any of the following commands:

Command Description
info View configuration of a specific project or summary of a specific bug
checkout Checkout a buggy or a fixed project version
compile Compile sources and developer-written tests of a buggy or a fixed project version
test Run a single test method or a test suite on a buggy or a fixed project version
mutation Run mutation analysis on a buggy or a fixed project version
coverage Run code coverage analysis on a buggy or a fixed project version
monitor.test Monitor the class loader during the execution of a single test or a test suite
export Export version-specific properties such as classpaths, directories, or lists of tests

Export version-specific properties

Use defects4j export -p <property_name> [-o output_file] in the working directory to export a version-specific property:

Property Description
classes.modified Classes (source files) modified by the bug fix
cp.compile Classpath to compile and run the project
cp.test Classpath to compile and run the developer-written tests
dir.src.classes Source directory of classes (relative to working directory)
dir.bin.classes Target directory of classes (relative to working directory)
dir.src.tests Source directory of tests (relative to working directory)
dir.bin.tests Target directory of test classes (relative to working directory)
tests.all List of all developer-written test classes
tests.relevant List of relevant tests classes (a test class is relevant if, when executed, the JVM loads at least one of the modified classes)
tests.trigger List of test methods that trigger (expose) the bug

Test execution framework

The test execution framework for generated test suites (framework/bin) provides the following scripts:

Script Description
defects4j Main script, described above
run_bug_detection Determine the real fault detection rate
run_mutation Determine the mutation score
run_coverage Determine code coverage ratios (statement and branch coverage)
run_evosuite Generate test suites using EvoSuite
run_randoop Generate test suites using Randoop

Mining and contributing additional bugs to Defects4J

The bug-mining README details the bug-mining process.

Additional resources

Scripts built on Defects4J

Fault localization (FL)

Automated program repair (APR)


  • "Defects4J: A Database of Existing Faults to Enable Controlled Testing Studies for Java Programs" René Just, Darioush Jalali, and Michael D. Ernst, ISSTA 2014 [download].

  • "Are Mutants a Valid Substitute for Real Faults in Software Testing?" René Just, Darioush Jalali, Laura Inozemtseva, Michael D. Ernst, Reid Holmes, and Gordon Fraser, FSE 2014 [download].

  • "Challenges in Using Search-Based Test Generation to Identify Real Faults in Mockito" Gregory Gay. SSBSE 2016 [download].

More publications

Implementation details

Documentation for any script or module is available as html documentation.

The directory structure of Defects4J is as follows:

   |--- project_repos:     The version control repositories of the provided projects.
   |--- major:             The Major mutation framework.
   |--- framework:         Libraries and executables of the core, test execution,
       |                   and bug-mining frameworks.
       |--- bin:           Command line interface to Defects4J.
       |--- bug-mining:    Bug-mining framework.
       |--- core:          The modules of the core framework.
       |--- lib:           Libraries used in the core framework.
       |--- util:          Util scripts used by Defects4J.
       |--- projects:      Project-specific resource files.
       |--- test:          Scripts to test the framework.

Versioning information

Defects4J uses a semantic versioning scheme (major.minor.patch):

Change major minor patch
Addition/Deletion of bugs X
New/upgraded internal or external tools X
Fixes and documentation changes X


MIT License, see license.txt for more information.

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