TARDIS

About

TARDIS (meTAheuRistically-driven DynamIc Symbolic execution) is an automatic test case generator for Java programs, aimed at achieving high branch coverage. It leverages a technique called dynamic symbolic (a.k.a. "concolic") execution, to alternate symbolic execution performed with the symbolic executor JBSE, with test case generation, performed by finding solutions to symbolic execution path constraints with the test case generator EvoSuite.

TARDIS aims at preserving the main advantages of SUSHI and, at the same time, improving performance when information on invariants is missing.

Installing TARDIS

There are two ways to install TARDIS. The easiest is via Docker; The less easy is by building it from source and deploying it on your local machine. In both cases we support only the head revision of the master branch. Formal releases will be available when TARDIS will be more feature-ready and stable.

Installing TARDIS via Docker

A convenient package is available from the TARDIS GitHub page, that allows you to install a Docker image containing a setup of TARDIS and some examples to play with. From the command line run:

$ docker pull ghcr.io/pietrobraione/tardis:master

Alternatively, download the Dockerfile to the current directory and from the command line run:

$ docker build -t tardis .
$ docker run -it tardis

The resulting environment is an Ubuntu container, where at the current (/root) directory you will find a clone of the head revision of the master branch of the TARDIS and of the tardis-experiments repositories.

Building TARDIS

TARDIS is composed by several projects, some of which are imported as git submodules, and is built with Gradle version 8.4, that is included in the repository. First, ensure that all the dependencies are present, including Z3 (see section "Dependencies"). Then, clone the TARDIS git repository and init/update its submodules. If you work from the command line, this means running first git clone, and then git submodule init && git submodule update. Next, follow the instructions described in the section "Patching the tests" of the README.md file of the JBSE subproject. Finally, run the build Gradle task, e.g. by invoking gradlew build from the command line.

Dependencies

TARDIS has many dependencies. It must be built using a JDK version 8 - neither less, nor more. We suggest to use the latest Eclipse Temurin from Adoptium v8 with HotSpot JVM (note that the JDK with the OpenJ9 JVM currently does not work, because there are some slight differences in the standard library classes). If you are on an Apple Silicon Mac we suggest to use the JDK Zulu distribution from Azul. The Gradle wrapper gradlew included in the repository will take care to select the right version of Java. Gradle will automatically resolve and use the following compile-time-only dependencies:

• JavaCC is used in the JBSE submodule for compiling the parser for the JBSE settings files.
• JUnit is used in the JBSE submodule for running the test suite that comes with JBSE (in future TARDIS might come with a test suite of its own).

The runtime dependencies that are automatically resolved by Gradle and included in the build path are:

• The tools.jar library, that is part of every JDK 8 setup (note, not of the JRE).
• Javassist, that is used by JBSE for all the bytecode manipulation tasks. The patched version of Javassist that is distributed with JBSE is necessary, and TARDIS will not work with an upstream Javassist version.
• args4j, that is used by TARDIS to process command line arguments.
• JavaParser, that is used by TARDIS to process the source files for the generated tests.
• Log4J 2, that is used by TARDIS for logging.

Another runtime dependency that is included in the git project is:

• EvoSuite; TARDIS depends on a customized version of EvoSuite that can be found in the libs subdirectory. It will not work with the upstream EvoSuite versions that you can download from the EvoSuite web page.

There is one additional runtime dependencies that is not handled by Gradle so you will need to fix it manually.

• JBSE needs to interact with an external numeric solver for pruning infeasible program paths. At the purpose TARDIS uses Z3, a standalone binary that can be installed almost everywhere in your system.

Finally, two runtime dependencies that are not currently used by TARDIS at runtime, but might be in future, are:

• JaCoCo, that is used by the coverage calculator included in SUSHI-Lib.
• ASM, that is a transitive dependency used by JaCoCo.

Gradle will download them to compile SUSHI-Lib, but you can avoid to deploy them.

Working under Eclipse

If you want to build (and possibly modify) TARDIS by using (as we do) the latest Eclipse for Java Developers, you are lucky: All the Eclipse plugins that are necessary to import and build TARDIS are already present in the distribution. The only caveat is that, since starting from version 2020-09 Eclipse requires at least Java 11 to run, your development machine will need to have both a Java 11 or greater (to run Eclipse) and a Java 8 setup (to build and run JBSE and TARDIS). Gradle will automatically select the right version of the JDK when building TARDIS. If you use a different flavor, or an earlier version, of Eclipse you might need to install the egit and the Buildship plugins, both available from the Eclipse Marketplace. After that, to import TARDIS under Eclipse follow these steps:

• To avoid conflicts we advise to import TARDIS under an empty workspace.
• Be sure that the default Eclipse JRE is the JRE subdirectory of a full JDK 8 setup, not a standalone (i.e., not part of a JDK) JRE. Do it as follows: From the main menu choose Eclipse > Preferences... under macOS, or Window > Preferences... under Windows and Linux. On the left panel select Java > Compiler and on the right combo box "Compiler compliance level" select "1.8". Then on the left panel select Java > Installed JREs... and on the right list tick the row corresponding to your JDK 8 setup (if it is not present, add it by pressing the "Add..." button).
• JBSE uses the reserved sun.misc.Unsafe class, a thing that Eclipse forbids by default. To avoid Eclipse complaining about that you must modify the workspace preferences as follows: From the main menu choose Eclipse > Preferences... under macOS, or Window > Preferences... under Windows and Linux. On the left panel select Java > Compiler > Errors/Warnings, then on the right panel open the option group "Deprecated and restricted API", and for the option "Forbidden reference (access rules)" select the value "Warning" or "Info" or "Ignore".
• Switch to the Git perspective. If you cloned the Github TARDIS repository and the submodules from the command line, you can import the clone under Eclipse by clicking under the Git Repositories view the button for adding an existing repository. Otherwise you can clone the repository by clicking the clone button, again available under the Git Repositories view (remember to tick the box "Clone submodules"). Eclipse does not want you to clone the repository under your Eclipse workspace, and instead wants you to follow the standard git convention of putting the git repositories in a git subdirectory of your home directory. If you clone the repository from a console, please follow this standard (if you clone the repository from the Git perspective Eclipse will do this for you).
• Switch back to the Java perspective and from the main menu select File > Import... In the Select the Import Wizard window that pops up choose the Gradle > Existing Gradle Project wizard and press the Next button twice. In the Import Gradle Project window that is displayed, enter in the Project root directory field the path to the TARDIS cloned git repository, and then press the Finish button to confirm. Now your workspace should have four Java project named jbse, sushi-lib, tardis, and tardis-master.
• Don't forget to apply all the patches as described at the beginning of the "Building TARDIS" section.
• Unfortunately the Buildship Gradle plugin is not able to fully configure the imported projects: As a consequence, after the import you will see some compilation errors due to the fact that the JBSE project did not generate some source files yet. Fix the situation by following this procedure: In the Gradle Tasks view double-click on the tardis > build > build task to build all the projects. Then, right-click the jbse project in the Package Explorer, and in the contextual menu that pops up select Gradle > Refresh Gradle Project. After that, you should see no more errors.

In the end, your Eclipse workspace should contain these projects:

• tardis: the container project from which Gradle must be run;
• tardis-master: the bulk of the TARDIS tool; on the filesystem it is in the master subdirectory;
• sushi-lib: the sushi-lib submodule for the run-time library component of TARDIS; on the filesystem it is in the runtime subdirectory;
• jbse: JBSE as a submodule; on the filesystem it is in the jbse subdirectory.

Deploying TARDIS

Deploying TARDIS outside the build environment to a target machine is tricky. The gradlew build command will produce a SUSHI-Lib jar runtime/build/libs/sushi-lib-<VERSION>.jar, the JBSE jars in jbse/build/libs (refer to the JBSE project's README file for more information on them), and a jar for the main TARDIS application master/build/libs/tardis-master-<VERSION>.jar. Moreover, it will copy all the dependencies of the SUSHI-Lib, JBSE and TARDIS projects in runtime/deps, jbse/deps, and master/deps respectively. You need to deploy all of them plus the native files (Z3). The build process will also produce an uber-jar master/build/libs/tardis-master-<VERSION>-shaded.jar containing all the runtime dependencies excluded EvoSuite, tools.jar, and the native files. Deploying based on the uber-jar is easier, but to our experience a setup based on the uber-jar is more crash-prone (on the other hand, using the uber-jar for JBSE is safe).

Here follow detailed instructions for deploying TARDIS based on the plain jars:

• Deploy Z3, possibly adding the Z3 binary to the system PATH.
• Deploy the tardis-master-<VERSION>.jar and set the Java classpath to point at it.
• Deploy either the jbse-<version>.jar or the jbse-<version>-shaded.jar and set the Java classpath to point at it. In the first case, also deploy the Javassist jar that you find in the jbse/libs directory, and set the Java classpath to point at it.
• Deploy the sushi-lib-<VERSION>.jar and set the Java classpath to point at it.
• Deploy the EvoSuite jar contained in the libs directory. While EvoSuite is run in separate processes, TARDIS will nevertheless try to load some of the EvoSuite classes, therefore you need to put the EvoSuite jar in the Java classpath.
• TARDIS requires a full JDK (not just a JRE) version 8 installed on the platform it runs. Add the tools.jar of the JDK 8 installed on the platform to the classpath.
• Deploy the args4j jar that you find in the Gradle cache. You will find a copy of it in the master/deps directory. This jar must be in the Java classpath.
• Deploy the javaparser-core jar that you find in the Gradle cache. You will find a copy of it in the master/deps directory. This jar must be in the Java classpath.
• Deploy the log4j-api jar that you find in the Gradle cache. You will find a copy of it in the master/deps directory. This jar must be in the Java classpath.
• Deploy the log4j-core jar that you find in the Gradle cache. You will find a copy of it in the master/deps directory. This jar must be in the Java classpath.

You can study the Dockerfile as an example of an automatic deployment workflow on Ubuntu.

If you deploy the tardis-master-<VERSION>-shaded.jar uber-jar you do not need to deploy the JBSE, SUSHI-Lib, args4j, Javaparser, Javassist and Log4J 2 jars.

Usage

Compile the target program with the debug symbols, then launch TARDIS either from the command line or from another program, e.g., from the main of an application. In the first case you need to invoke it as follows:

$ java -Xms16G -Xmx16G -cp <classpath> tardis.Main <options>

where <classpath> must be set according to the indications of the previous section. (Note that TARDIS is resource-consuming, thus we increased to 16 GB the memory allocated to the JVM running it). If you prefer to invoke TARDIS programmatically, this is a possible template of a launcher class:

import tardis.Main;
import tardis.Options;

public final class Launcher {
  public static void main(String[] args) {
    final Options o = new Options();
    o.setZ3Path(...);
    o.setTargetClass(...);
    ...
    final Main m = new Main(o);
    m.start();
  }
}

The launcher must create a tardis.Options object, configure it with the necessary options, then it must create a tardis.Main object and pass to its constructor the previously configured tardis.Options object. Finally, it must invoke the tardis.Main.start() method. Note that the command line TARDIS launcher is not much different from this example, the main difference being that the command line launcher parses the command line arguments to create the tardis.Options object.

Shall you launch TARDIS via the command line or programmatically, you will need to set a number of options for it to work. The indispensable ones, that you must set in order to obtain any result, are:

• -java8_home (command line) or setJava8Home (tardis.Options): the path to the home directory of a Java 8 full JDK setup, in case the default JDK installed on the deploy platform is not Java 8, or should be overridden. If this parameter is not provided, TARDIS will try with the default JDK installed on the deploy platform.
• -evosuite (command line) or setEvosuitePath (tardis.Options): the path to the EvoSuite jar file evosuite-shaded-1.2.1-SNAPSHOT.jar contained in the libs/ folder. The same jar file must be put on the classpath (see previous section).
• -jbse_lib (command line) or setJBSELibraryPath (tardis.Options): this must be set to the path of the JBSE jar file from the jbse/build/libs directory. It must be the same you put in the classpath. If you chose to deploy the tardis-master-<VERSION>-shaded.jar uber-jar, set this option to point to it.
• -sushi_lib (command line) or setSushiLibPath (tardis.Options): this must be set to the path of the SUSHI-Lib jar file from the runtime/build/libs directory. If you chose to deploy the tardis-master-<VERSION>-shaded.jar uber-jar, set this option to point to it.
• -z3 (command line) or setZ3Path (tardis.Options): the path to the Z3 binary.
• -classes (command line) or setClassesPath (tardis.Options): a colon- or semicolon-separated (depending on the OS) list of paths; It is the classpath of the software under test.
• -target_class (command line) or setTargetClass (tardis.Options): the name in internal classfile format of the class to test: TARDIS will generate tests for all the methods in the class. Or alternatively:
• -target_method (command line) or setTargetMethod (tardis.Options): the signature of a method to test. The signature is a colon-separated list of: the name of the container class in internal classfile format; the descriptor of the method; the name of the method. You can use the javap command, included with every JDK setup, to obtain the internal format signatures of methods: javap -s my.Class prints the list of all the nonprivate methods in my.Class with their signatures in internal format.
• -tmp_base (command line) or setTmpDirectoryBase (tardis.Options): a path to a temporary directory; TARDIS needs to create many intermediate files, and will put them in a subdirectory of the one that you specify with this option. The subdirectory will have as name the date and time when TARDIS was launched.
• -out (command line) or setOutDirectory (tardis.Options): a path to a directory where TARDIS will put the generated tests.
• -evosuite_no_dependency (command line) or setEvosuiteNoDependency (tardis.Options): when active, the generated test classes will not depend on the EvoSuite jar (i.e., no scaffolding class will be generated).

There are many more options that allow to control several aspects of TARDIS behaviour. You can see a synthetic description of all of them by invoking TARDIS from the command line with the -help option.

A possible example of command line invocation is the following:

$ java -Xms16G -Xmx16G -cp /usr/lib/jvm/java-8-openjdk-amd64/lib/tools.jar:./libs/tardis-master-0.2.0-SNAPSHOT.jar:./libs/sushi-lib-0.2.0-SNAPSHOT.jar:./libs/jbse-0.11.0-SNAPSHOT-shaded.jar:./libs/evosuite-shaded-1.2.1-SNAPSHOT.jar:./libs/args4j-2.32.jar:./libs/log4j-api-2.14.0.jar:./libs/log4j-core-2.14.0.jar:./libs/javaparser-core-3.15.9.jar tardis.Main -jbse_lib ./libs/jbse-0.11.0-SNAPSHOT-shaded.jar -sushi_lib ./libs/sushi-lib-0.2.0-SNAPSHOT.jar -evosuite ./libs/evosuite-shaded-1.2.1-SNAPSHOT.jar -z3 /usr/bin/z3 -classes ./my-application/bin -target_class my/Class -tmp_base ./tmp -out ./tests

where we assume that all the jars except for tools.jar are in ./libs, that the software to be tested is in ./my-application/bin, that the class to generate tests for is my.Class, that a work directory where TARDIS can put intermediate files is ./tmp, and that we want TARDIS to emit the generated tests in ./tests. In the case you prefer (at your own risk) to use the TARDIS uber-jar the command line invocation becomes a bit, but not that much, shorter:

$ java -Xms16G -Xmx16G -cp /usr/lib/jvm/java-8-openjdk-amd64/lib/tools.jar:./libs/tardis-master-0.2.0-SNAPSHOT-shaded.jar:./libs/evosuite-shaded-1.2.1-SNAPSHOT.jar tardis.Main -jbse_lib ./libs/tardis-master-0.2.0-SNAPSHOT-shaded.jar -sushi_lib ./libs/tardis-master-0.2.0-SNAPSHOT-shaded.jar -evosuite ./libs/evosuite-shaded-1.2.1-SNAPSHOT.jar -z3 /usr/bin/z3 -classes ./my-application/bin -target_class my/Class -tmp_base ./tmp -out ./tests

There is a third way of launching TARDIS that mixes the two approaches: You can launch it from the command line, but by configuring the options through an object of class tardis.Options. At the purpose you must define a class implementing the interface tardis.OptionsConfigurator. This interface declares only one method configure, that you must override to configure a tardis.Options object as in the following example:

import tardis.Options;
import tardis.OptionsConfigurator;

public final class MyConfigurator implements OptionsConfigurator {
  @Override
  public void configure(Options o) {
    o.setZ3Path(...);
    o.setTargetClass(...);
    ...
  }
}

As you can see, the resulting code resembles that of a TARDIS launcher, but you do not need to explicitly create the tardis.Options object (it is received as a parameter) nor to create the tardis.Main object and start it. Once created your configurator class, compile it (remember to put the tardis-master jar in the compilation classpath), put the generated classfile where you prefer and invoke TARDIS as follows:

$ java -Xms16G -Xmx16G -cp /usr/lib/jvm/java-8-openjdk-amd64/lib/tools.jar:./libs/tardis-master-0.2.0-SNAPSHOT.jar:./libs/sushi-lib-0.2.0-SNAPSHOT.jar:./libs/jbse-0.11.0-SNAPSHOT-shaded.jar:./libs/evosuite-shaded-1.2.1-SNAPSHOT.jar:./libs/args4j-2.32.jar:./libs/log4j-api-2.14.0.jar:./libs/log4j-core-2.14.0.jar:./libs/javaparser-core-3.15.9.jar tardis.Main -options_config_path ./my-config -options_config_class MyConfigurator

(here we assume that we put the MyConfigurator.class classfile in the ./my-config directory). You will find examples of both launcher and configurator classes in the tardis-experiments project.

Running TARDIS from the Docker environment

Under the Docker environment you can find a more convenient tardis script that is installed on the PATH. When invoked, it runs java, passes to it the classpath and some of the indispensable options, and starts tardis.Main. This allows you to invoke TARDIS as follows:

$ tardis <options>

relieving you from most of the command line boilerplate. More precisely, you do not need to pass the -java8_home, -evosuite, -jbse_lib, -sushi_lib and -z3 options, because the script does it already for you. This way the previous example commands become much shorter:

$ tardis -classes ./my-application/bin -target_class my/Class -tmp_base ./tmp -out ./tests

with the options on the command line, and

$ tardis -options_config_path ./my-config -options_config_class MyConfigurator

with the configurator classes. The tardis script is at /usr/local/bin in the case you want to study it.

If you want to run TARDIS on the pre-built tardis-experiments subjects included in the Docker image you can exploit the configurators and the launchers included in the tardis-experiments project. For instance, if you want to generate tests for the AVL tree example, you can run the following command using the configurator:

$ tardis -options_config_path /root/tardis-experiments/bin -options_config_class avl.AvlConfigurator

or you can invoke the launcher as follows:

$ java -cp ${CLASSPATH}:/root/tardis-experiments/bin avl.RunAvl

See the README.md file of the tardis-experiment project for more information on where the configurators and the launchers are. TARDIS will put the generated tests in /root/tardis-experiments/tardis-test and the intermediate files in a subdirectory of /root/tardis-experiments/tardis-out.

Generated tests

The generated tests are in EvoSuite format, where a test suite is composed by two classes: a scaffolding class, and a class containing the actual test cases (the actual suite). In case the -evosuite_no_dependency option is active, the scaffolding class will not be generated, and the suite will be composed by the actual suite class only: Note, however, that without scaffolding the tests might be flaky. TARDIS will produce many suites each containing exactly one test case: If, e.g., a run of TARDIS generates 10 test cases, then in the directory indicated with the -out command line parameter you will find 10 scaffolding classes, and 10 actual test suite classes each containing exactly 1 test case. Note that all these classes depend on the JUnit and EvoSuite jars, therefore you will need to put these jars on the classpath when compiling and running the test suites. If the -evosuite_no_dependency option is active, the tests will not depend on EvoSuite so you will not need to put the EvoSuite jar on the classpath.

The names of the generated files are structured as follows:

<class name>_<number>_Test_scaffolding.java //the scaffolding class
<class name>_<number>_Test.java             //the actual suite class

where <class name> is the name of the class under test, and <number> is a sequential number that distinguishes the different generated classes, and that roughly reflects in which order the tests were generated.

The generated scaffolding/actual suite classes are declared in the same package as the class under test, so they can access its package-level members. This means, for example, that if you have specified the option -out /your/out/dir, an avl_tree.AvlTree class under test will produce a test /your/out/dir/avl_tree/AvlTree_1_Test.java. If you want to compile and execute the test suites add the output directory to the classpath and qualify the class name of the test suite with the package name, e.g.:

$ javac -cp junit.jar:evosuite-shaded-1.2.1-SNAPSHOT.jar:avltree.jar /your/out/dir/avl_tree/AvlTree_1_Test.java
$ java -cp junit.jar:evosuite-shaded-1.2.1-SNAPSHOT.jar:avltree.jar:/your/out/dir org.junit.runner.JUnitCore avl_tree.AvlTree_1_Test

Disclaimer

TARDIS is a research prototype. As such, it is more focused on functionality than on usability. We are committed to progressively improving the situation.