A Database of Real Faults and an Experimental Infrastructure to Enable Controlled Experiments in Software Engineering Research
Perl Shell Java


Defects4J -- version 1.2.0 Build Status

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

The projects

Defects4J contains 395 bugs from the following open-source projects:

Identifier Project name Number of bugs
Chart JFreeChart 26
Closure Closure compiler 133
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 -- the Defects4J maintainers manually pruned out irrelevant changes (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).


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

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.

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

Getting started

Setting up Defects4J

  1. Clone Defects4J:

    • git clone https://github.com/rjust/defects4j
  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
    • ./init.sh
  3. Add Defects4J's executables to your PATH:

    • export PATH=$PATH:"path2defects4j"/framework/bin

Using Defects4J

  1. Check installation and 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. More examples of how to use the framework are available in framework/test


  • "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].


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

Command-line interface

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)
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
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
^Note that this script requires Perl DBI.

Directory structure

This is the top-level directory of Defects4J. The directory structure is as follows:

   |--- project_repos:     The version control repositories of the provided projects.
   |--- major:             The Major mutation framework.
   |--- framework:         Libraries and executables of the database abstraction and
       |                   test execution framework.
       |--- bin:           Command line interface to Defects4J.
       |--- 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.

Additional resources

Fault localization (FL)

Automated program repair (APR)


MIT License, see license.txt for more information.