JUnit and Surefire Parallel Tests - ForkCount & ThreadCount

You have to provide explicit junit test provider:

<plugin>    <groupId>org.apache.maven.plugins</groupId>    <artifactId>maven-surefire-plugin</artifactId>    <version>2.18.1</version>    <dependencies>        <dependency>            <groupId>org.apache.maven.surefire</groupId>            <artifactId>surefire-junit47</artifactId>            <version>2.18.1</version>        </dependency>    </dependencies>    <configuration>        <parallel>all</parallel>        <useUnlimitedThreads>true</useUnlimitedThreads>        <useSystemClassLoader>false</useSystemClassLoader>        <includes>            <include>${testSuite}</include>        </includes>        <systemPropertyVariables>            <browser>${browser_type}</browser>        </systemPropertyVariables>     </configuration></plugin>

And you should use JUnit 4.7+ as older versions does not work with parallel testing correctly.

Also you can omit fork-related parameters if your tests do NOT affect JVM runtime (usually it's not the case).

Or migrate your tests to TestNG - it is more elegant framework and it works with parallel testing much better, then JUnit (imo).

There are so many configuration for running test in parallel.

According to the documentation:

forkCount

The parameter forkCount defines the maximum number of JVM processes that Surefire will spawn concurrently to execute the tests. It supports the same syntax as -T in maven-core: if you terminate the value with a C, that value will be multiplied with the number of available CPU cores in your system. For example forkCount=2.5C on a Quad-Core system will result in forking up to ten concurrent JVM processes that execute tests.

...

The default setting is forkCount=1/reuseForks=true, which means that Surefire creates one new JVM process to execute all tests in one maven module.

threadCount

When using reuseForks=true and a forkCount value larger than one, test classes are handed over to the forked process one-by-one. Thus, parallel=classes would not change anything. However, you can use parallel=methods: classes are executed in forkCount concurrent processes, each of the processes can then use threadCount threads to execute the methods of one class in parallel.

As fair as I understand, threadCount is like a sub threading for each fork.

You can tweak these params to improve your test performance, for instance you can have:

<plugin>    <groupId>org.apache.maven.plugins</groupId>    <artifactId>maven-surefire-plugin</artifactId>    <version>2.17</version>    <configuration>         <includes>              <include>${testSuite}</include>         </includes>         <parallel>all</parallel>         <useSystemClassLoader>false</useSystemClassLoader>         <perCoreThreadCount>false</perCoreThreadCount>         <forkCount>2.0C</forkCount>         <reuseForks>true</reuseForks>         <threadCount>20</threadCount>         <browser>${browser_type}</browser>    </configuration></plugin>

You can find more details in its site:

https://maven.apache.org/surefire/maven-surefire-plugin/examples/fork-options-and-parallel-execution.html