Tutorial Part 2: Maven integration

What you will learn in this tutorial

  • Setting up Maven projects to run EvoSuite tests
  • Generating tests from Maven
  • Updating generated tests with Maven
  • Making EvoSuite part of continuous integration

Preparing the project under test

For the second part of the tutorial, we will be testing a simple library consisting of a couple of (dummy) container classes, including the Stack implementation from part 1. Please download and extract the archive containing this example:

wget http://evosuite.org/files/tutorial/Tutorial_Maven.zip
unzip Tutorial_Maven.zip

Change into the main directory again, which is where we will be running Maven and EvoSuite:

cd Tutorial_Maven

As previously, we can compile the classes in the project using the following command:

mvn compile

This puts the compiled bytecode of these classes in the target/classes directory. Make sure that this worked correctly.

There are some tests included in src/test/java, which we can run using the following command:

mvn test

If this works correctly, you should see something like this:

 T E S T S
 Running tutorial.StackTest
 Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.094 sec

 Results :

 Tests run: 1, Failures: 0, Errors: 0, Skipped: 0

 [INFO] ------------------------------------------------------------------------
 [INFO] ------------------------------------------------------------------------
 [INFO] Total time: 3.799 s
 [INFO] Finished at: 2016-04-04T10:08:03+01:00
 [INFO] Final Memory: 16M/142M
 [INFO] ------------------------------------------------------------------------

If this worked correctly, then you are ready to integrate EvoSuite. In order to do this, we need to have a closer look at how to configure Maven.

A closer look at the pom.xml file

If you are already well familiar with Maven this section will likely not tell you anything new. However, it is important to understand how to configure Maven projects in order to configure the project to use EvoSuite. Therefore, we will now take a closer look at the main Maven configuration file of our example project, which is the file pom.xml.

The pom.xml in our example project is based on a basic version generated using mvn archetype:generate. It starts with some basic meta-information about the project:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">



Besides some generic stuff (e.g., URL and name of the project) the main aspects are groupId, artifactId, and version. Maven idenfifies projects using these three items. This is important to know when it comes to declaring dependencies. Our example project currently has one dependency, which is JUnit to execute the tests. This is declared in the <dependency> section:


As you can see, junit is identified by its groupId, artifactId, and version, like we defined for our project above. The scope defines that this dependency is only needed when running tests, not for compiling or executing the project itself.

Generating EvoSuite tests with Maven

The dependencies section only declares what the code we are working with depends on. However, what we would like to do is to tell Maven that we would like to use EvoSuite as part of our build – so we need to declare a build dependency on EvoSuite, not a project dependency. Dependencies of the build are specified as plugins in the build section of the pom.xml. Add the following snippet to the pom.xml as a child node of <project>, for example beneath the </dependencies> section:


What this tells Maven is that during our build, we want to make use of the EvoSuite Maven plugin. Maven can automatically resolve build dependencies just like it resolves project dependencies, by looking for a plugin with the given groupId, artifactId, and version on Maven central.

At this point, one caveat is that the EvoSuite plugin is not yet available on Maven Central. Therefore, we need to tell Maven that it should also look at EvoSuite’s Maven repository when trying to resolve dependencies. To achieve this, we need to add a <pluginRepositories> section where we specify EvoSuite’s URL:

    <name>EvoSuite Repository</name>

The <pluginRepositories> section is again a child of the <project> tag, so for example you could add it at the end, before the closing </project> tag.

Now we can check if our setup works correctly by invoking the Evosuite plugin. The plugin is called evosuite, and as is normal for Maven plugins, we call it by providing the plugin name separated with a colon from the plugin goal. For example, if we want to execute the plugin goal help of the evosuite plugin, we would type the following command:

mvn evosuite:help

The first time you invoke the EvoSuite plugin, Maven will download EvoSuite and its dependencies and this may take a while. Once everything is downloaded, you should see the following help message:

[INFO] --- evosuite-maven-plugin:1.0.6:help (default-cli) @ Tutorial_Maven ---
[INFO] Maven Plugin for EvoSuite 1.0.6
  Plugin used to run EvoSuite to automatically generate high coverage JUnit

  This plugin has 7 goals:

    Remove all local files created by EvoSuite so far

    Execute the manually written test suites (usually located under src/test/java)
    and return the coverage of each class.

    When run, EvoSuite generate tests in a specific folder. New runs of EvoSuite
    can exploit the tests in such folder, and/or modify them.

    So, with 'export' we can copy all generated tests to a specific folder, which
    by default points to where Maven searches for tests. If another folder is
    rather used (or if we want to run with Maven the tests in the default EvoSuite
    folder), then Maven plugins like build-helper-maven-plugin are needed

    Generate JUnit tests

    Display help information on evosuite-maven-plugin.
    Call mvn evosuite:help -Ddetail=true -Dgoal=<goal-name> to display parameter

    Obtain info of generated tests so far

    Workaround mojo to overcome bug in Maven. Needed when EvoSuite tests are run
    together with manual ones

[INFO] ------------------------------------------------------------------------
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1.489 s
[INFO] Finished at: 2016-04-04T10:55:45+01:00
[INFO] Final Memory: 9M/109M
[INFO] ------------------------------------------------------------------------

If you don’t see this but get to see an error message, then likely there is a problem in your pom.xml. Make sure you copied all the above additions to the pom.xml correctly and try again.

We can set properties for our plugin goals just like we would set properties for any Java process, using the -Dproperty=value syntax. For example, to get more detailed information about the generate plugin goal when executing the help plugin goal, we can run the following command:

mvn evosuite:help -Ddetail=true -Dgoal=generate

If you run this command, you should see a list of all the properties that you can set for the generate plugin goal.

Let’s waste no more time and generate some tests! Type:

mvn evosuite:generate

If EvoSuite is set up correctly, you should see something similar to the following output:

[INFO] --- evosuite-maven-plugin:1.0.6:generate (default-cli) @ Tutorial_Maven ---
[INFO] Going to generate tests with EvoSuite
[INFO] Total memory: 800mb
[INFO] Time per class: 2 minutes
[INFO] Number of used cores: 1
[INFO] Target: /Users/gordon/Documents/Papers/evosuite-tutorial/CommandLine/Tutorial_Maven/target/classes
[INFO] Basedir: /Users/gordon/Documents/Papers/evosuite-tutorial/CommandLine/Tutorial_Maven
[INFO] Started spawn process manager on port 64917
[INFO] * EvoSuite 1.0.6
[INFO] Registered remote process from /
[INFO] Going to execute 4 jobs
[INFO] Estimated completion time: 8 minutes, by 2016-04-04T11:09:06.277
[INFO] Going to start job for: tutorial.LinkedList. Expected to end in 190 seconds, by 2016-04-04T11:04:16.336

The output tells us that EvoSuite will generate tests for 4 classes, which it estimates to take around 8 minutes. The first job it started is the class tutorial.LinkedList. Now is the time to wait and get some coffee, until Evosuite has finished testing all the classes.

If you have a powerful machine with multiple cores, you can also parallelise the EvoSuite jobs in order to save time. For example, to run 4 EvoSuite jobs in parallel you could add the -Dcores=4 property to the evosuite:generate command:

mvn -Dcores=4 evosuite:generate

Integrating generated tests into the source tree

If everything goes well, you should see a BUILD SUCCESS message from Maven when EvoSuite is done. If so, then congratulations, you just generated some test suites with the EvoSuite Maven plugin! If you do not see that message, then something went wrong – please check the error message and make sure you have set up the Maven project correctly.

So, what have we generated? To find out the current state of what EvoSuite has generated for us, use the following command:

mvn evosuite:info

As we have just invoked EvoSuite on 4 classes, you should get an output like this:

[INFO] --- evosuite-maven-plugin:1.0.6:info (default-cli) @ Tutorial_Maven ---
[INFO] Going to query EvoSuite info on current project
[INFO] * EvoSuite 1.0.6
[INFO] Total number of classes in the project: 4
[INFO] Number of classes in the project that are testable: 4
[INFO] Number of generated test suites: 4
[INFO] Overall coverage: 0.99
[INFO] ------------------------------------------------------------------------

We’ve got a test suite for each of our classes, and the coverage is great. But, where are these test suites?

Right now, they are in a hidden directory .evosuite. This is a directory where EvoSuite keeps information, in order to improve test generation over time. For example, if a class hasn’t changed and we already have a test suite, we don’t want to invoke EvoSuite on it again – but more about this later. For now, you can see what EvoSuite has put into .evosuite; in particular, you will find the generated tests in .evosuite/best-tests:

ls .evosuite/best-tests/tutorial

This should show you 8 files – 4 test suites, and 4 scaffolding files:

LinkedListIterator_ESTest.java          Node_ESTest.java
LinkedListIterator_ESTest_scaffolding.java  Node_ESTest_scaffolding.java
LinkedList_ESTest.java              Stack_ESTest.java
LinkedList_ESTest_scaffolding.java      Stack_ESTest_scaffolding.java

Assuming you are happy with these test suites, we can integrate them into the source tree. By default, JUnit tests are expected to be located in src/test/java in Maven projects, so this is where EvoSuite will put the test suites. To do this, invoke the following command:

mvn evosuite:export

You should now have the test suites copied over to src/test/java – make sure they are there.

Executing EvoSuite tests with Maven

Now that we have these tests in our source tree, it would be great to execute them. With Maven, this is done by invoking the test lifecycle phase:

mvn test

However, if you try this now, what you will see are plenty of error messages about package org.evosuite.runtime does not exist. Recall that EvoSuite tests have a dependency on the EvoSuite runtime library, because they do bytecode instrumentation and all sorts of other stuff to avoid flaky tests. Therefore, we need to tell Maven to use this runtime library. We already know how to add dependencies to Maven projects; this time it is a project dependency, and so we add a new item to the <dependencies> tag in your pom.xml:


Once you’ve done that, try executing the tests again:

mvn test

If you set up everything correctly, you should see output similar to this one:

 T E S T S
 Running tutorial.LinkedList_ESTest
 Tests run: 10, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 2.192 sec
 Running tutorial.LinkedListIterator_ESTest
 Tests run: 6, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.356 sec
 Running tutorial.Node_ESTest
 Tests run: 5, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.024 sec
 Running tutorial.Stack_ESTest
 Tests run: 9, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.051 sec
 Running tutorial.StackTest
 Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.001 sec

 Results :

 Tests run: 31, Failures: 0, Errors: 0, Skipped: 0

Note that the number of tests will vary inevitably – EvoSuite uses a randomized algorithm to generate tests, so every time you invoke it you will get a different result.

Keeping EvoSuite tests separate from developer-written tests

When we exported the tests using mvn evosuite:export they were copied to src/test/java, which is where Maven expects all tests to be. Sometimes, developers may prefer to keep their own tests separated from generated tests.

Let’s assume we do not want the generated tests in src/test/java. Remove the tests we have already exported there:

rm src/test/java/*ESTest*.java

The export goal offers a property to specify where to export tests to – recall that we can get details about this goal by using the following command:

mvn evosuite:help -Ddetail=true -Dgoal=export

The output reveals the property we are looking for:

Available parameters:

  targetFolder (Default: src/test/java)

    User property: targetFolder

There are two ways we can specify the targetFolder. The first one is to do so explicitly on the command line:

    mvn evosuite:export -DtargetFolder=src/test/evosuite

Alternatively, we can specify it in the pom.xml as part of the <properties> section. Add the following entry (as a child to <project>):


Now, try exporting EvoSuite tests again:

mvn evosuite:export

You should now see your tests exported to src/test/evosuite rather than src/test/java. Great!

However, not quite so great yet: If we run mvn test then this will by default not include src/test/evosuite, and will just execute our existing test:

 T E S T S
Running tutorial.StackTest
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.079 sec

Results :

Tests run: 1, Failures: 0, Errors: 0, Skipped: 0

We thus need to tell it where to find our tests. Add the following plugin configuration to the <plugins> section of the <build> part of the pom.xml:


After this change, try running the tests again:

mvn test

This time, the tests in src/test/evosuite should be compiled and executed together with the other tests.

Executing EvoSuite tests together with developer written tests

Although our tests executed nicely together with the existing tests, there is potential for problems: As you already know, EvoSuite instruments the code under test heavily in order to avoid flaky tests. If manually written tests are executed in the same process, they will use the same instrumented versions of the classes. To make sure that the instrumentation is only active for EvoSuite tests, we need to add an initializing listener for the EvoSuite tests. To do this, add the following section to the <plugins> section in the <build> part of the pom.xml file:


In our small example you will not see a difference, but in practice you might.