surefire-plugin does not respect threadCount parameter - maven

Question

Since several days, I tried to see where is my mistake in my configuration to run in parallel my Selenium tests.
I have a Selenium Grid with 2 nodes.
In my pom.xml, I have set surefire to run 2 by 2 the methods of my tests with a particular category then other tests.
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.18.1</version>
<executions>
<execution>
<id>default-test</id>
<goals>
<goal>test</goal>
</goals>
<configuration>
<parallel>methods</parallel>
<perCoreThreadCount>false</perCoreThreadCount>
<threadCount>2</threadCount>
<reuseForks>false</reuseForks>
<groups>
com.something.categories.Safe,
com.something.categories.Parallel
</groups>
</configuration>
</execution>
<execution>
<id>no-safe</id>
<goals>
<goal>test</goal>
</goals>
<configuration>
<excludedGroups>
com.something.categories.Safe,
com.something.Parallel
</excludedGroups>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
When I launch my test mvn clean test -Dtest='TestAwesome' all the tests contains in TestAwesome are launched in the same time (I see more than 2 browsers opended), and so does not respect my threadCount value.
I'm missing something?
Edition after answer
Here my partial pom.xml to solve my issue
<profiles>
<profile>
<id>selenium-tests</id>
<activation>
<activeByDefault>true</activeByDefault>
</activation>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.18.1</version>
<configuration>
<parallel>all</parallel>
<threadCount>${threads}</threadCount>
<perCoreThreadCount>false</perCoreThreadCount>
<useUnlimitedThreads>true</useUnlimitedThreads>
<systemProperties>
<browser>${browser}</browser>
<screenshotDirectory>${project.build.directory}/screenshots</screenshotDirectory>
<gridURL>${seleniumGridURL}</gridURL>
<env>${env}</env>
</systemProperties>
<groups>${groups}</groups>
<excludedGroups>${excludedGroups}</excludedGroups>
</configuration>
</plugin>
</plugins>
</build>
</profile>
</profiles>

Answer 1

Since you are using a modern-enough version of surefire, you might wanna try the threadCountMethods parameter instead of threadCount in combination with useUnlimitedThreads = true, even though it seems counter-intuitive.
surefire jUnit examples:
As of Surefire 2.7, no additional dependencies are needed to use the full set of options with parallel. As of Surefire 2.16, new thread-count attributes are introduced, namely threadCountSuites, threadCountClasses and threadCountMethods.
Fork options and parallel execution:
As an example with an unlimited number of threads, there is maximum of three concurrent threads to execute suites: parallel = all, useUnlimitedThreads = true, threadCountSuites = 3.