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EvoMaster Driver

To generate tests for white-box testing, you need an EvoMaster Driver up and running before executing evomaster.jar. These drivers have to be built manually for each system under test (SUT). See the EMB repository for a set of existing SUTs with drivers.

To build a client driver in Java (or any JVM language), you need to import the EvoMaster Java client library. For example, in Maven:


For the latest version, check Maven Central Repository. The latest version number should also appear at the top of the main readme page. If you are compiling directly from the EvoMaster source code, make sure to use mvn install to install the snapshot version of the Java client into your local Maven repository (e.g., under ~/.m2).

Once the client library is imported, you need to create a class that extends either or Both these classes extend SutController. The difference is on whether the SUT is started in the same JVM of the EvoMaster driver (embedded), or in a separated JVM (external).

The easiest approach (which we recommend) is to use the embedded version, especially when dealing with frameworks like Spring and DropWizard. However, when the presence of the EvoMaster client library gives side-effects (although its third-party libraries are shaded, side-effects might still happen), or when it is not possible (or too complicate) to start the SUT directly (e.g., JEE), it is better to use the external version. The requirement is that there should be a single, self-executable uber/fat jar for the SUT (e.g., Wildfly Swarm). It can be possible to handle WAR files (e.g., by using Payara), but currently we have not tried it out yet.

Once a class is written that extends either EmbeddedSutController or ExternalSutController, there are a few abstract methods that need to be implemented. For example, those methods specify how to start the SUT, how it should be stopped, and how to reset its state. The EvoMaster Java client library also provides further utility classes to help writing those controllers/drivers. For example, helps in resetting the state of a database (if any is used by the SUT).

Once a class X that is a descendant of SutController is written, you need to be able to start the EvoMaster driver, by using the class. For example, in the source code of the class X, you could add:

public static void main(String[] args){

   SutController controller = new X();
   InstrumentedSutStarter starter = new InstrumentedSutStarter(controller);


At this point, once this driver is started (e.g., by right-clicking on it in an IDE to run it as a Java process), then you can use evomaster.jar to finally generate test cases.

WARNING: Java 9 broke backward compatibility. One painful change was that self-attachment of Java-Agents (needed for bytecode instrumentation) is now forbidden by default. When for example starting the driver with a JDK 9+ (e.g., JDK 11), you need to add the VM option -Djdk.attach.allowAttachSelf=true, otherwise the process will crash.
For example, in IntelliJ IDEA:

Note: there is a hacky workaround for this "feature" (i.e., as done in ByteBuddy), but it is not implemented yet.

SpringBoot Example

How to start/reset/stop the SUT depends on the chosen framework used to implement the SUT. To implement an EvoMaster Driver class, you need check the JavaDocs of the extended super class, e.g., EmbeddedSutController, and the existing examples in EMB.

As SpringBoot is nowadays the most common way to implement enterprise systems on the JVM, here we provide some discussions / walk-through on how to write a driver for it that extends EmbeddedSutController, using as reference the driver for the features-service SUT in EMB.

To programmatically start a SpringBoot application (needed to implement startSut()), you can use, and save the resulting ConfigurableApplicationContext in variable (e.g., ctx). This will be useful when needing to override the methods isSutRunning() and stopSut(), as you can just implement them with ctx.isRunning() and ctx.stop().

When starting the SUT, there are at least two configurations that you want to change:

  • the binding port, as you want to use 0 for ephemeral ports (to avoid port conflicts).
  • if the SUT is using a SQL database, you MUST wrap the SQL driver with P6Spy. This is as simple as adding :p6spy in the connecting datasource URL and change the driver-class-name. This is needed by EvoMaster to be able intercept and analyse all the interactions with the database.

For a SUT like features-service, this can be done with:

ctx =, new String[]{
                "--spring.datasource.driver-class-name=" + P6SpyDriver.class.getName(),

The actual chosen port can then be extracted with:

protected int getSutPort() {
        return (Integer) ((Map) ctx.getEnvironment()

Finally, the startSut() method must return the URL of where the SUT is listening on. When running tests locally, this is as simple as returning "http://localhost:" + getSutPort().

If the application is using a SQL database, you must configure getConnection() and getDatabaseDriverName(), instead of leaving their returned values as null. For example, if you are using H2, then the driver name would be org.h2.Driver. In SpringBoot, you can extract a connection object in the startSut() method (and save it in a variable), by simply using:

JdbcTemplate jdbc = ctx.getBean(JdbcTemplate.class);
connection = jdbc.getDataSource().getConnection();

Test cases must be independent from each other. Otherwise, you could get different results based on their execution order. To enforce such independence, you must clean the state of the SUT in the resetStateOfSUT() method. In theory, RESTful APIs should be stateless. If indeed stateless, resetting the state would be just a matter of cleaning the database. For this purpose, we provide the DbCleaner utility class (used to delete data without recreating the database schema). There might be some tables that you might not want to clean, like for example if you are using FlyWay to handle schema migrations. These tables can be skipped, for example:

public void resetStateOfSUT() {
   DbCleaner.clearDatabase_H2(connection, Arrays.asList("schema_version"));

where the content of the table schema_version is left untouched.

If your application uses some caches, those might be reset at each test execution. However, an easier approach could be to just start the SUT without the caches, for example using the option --spring.cache.type=NONE.

When EvoMaster evolves test cases, it tries to maximize code coverage in the SUT. But there is no much point in trying to maximize code coverage of the third-party libraries, like Spring, Hibernate, Tomcat, etc. Therefore, in the getPackagePrefixesToCover() you need to specify the common package prefix for your business logic. In the case of the features-service SUT, this was org.javiermf.features.

To test a RESTful API, in the the getProblemInfo(), you need to return an instance of the RestProblem class. Here, you need to specify where the OpenApi schema is found, and whether any endpoint should be skipped, i.e., not generating test cases for. This latter option is useful for example to skip the SpringBoot Actuator endpoints (if any is present).
If your RESTful API does not have an OpenApi/Swagger schema, this can be automatically added by using libraries such as SpringFox and SpringDoc.

The SUT might require authenticated requests (e.g., when Spring Security is used). How to do it must be specified in the getInfoForAuthentication(). We support auth based on authentication headers and cookies. The can be used to simplify the creation of such configuration objects, e.g., by using methods like getForDefaultSpringFormLogin().

Although EvoMaster can read and analyze the content of a SQL database, it cannot reverse-engineer the hashed passwords. These must be provided with getInfoForAuthentication(). If such auth info is stored in a SQL database, and you are resetting the state of such database in the resetStateOfSUT() method, you will need there to recreate the login/password credentials as well. You could write such auth setup in a init_db.sql SQL script file, and then in resetStateOfSUT() execute:

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