Maven: how to set thread count for testng - multithreading

Question

I'm using testng to run tests in parallel. Xml file contains thread-count parameter.
<suite name="Lalala" parallel="tests" thread-count="3" preserve-order="true">
But I want to set the thread-count value from POM file. I tried
<dependency>
<groupId>org.testng</groupId>
<artifactId>testng</artifactId>
<version>6.3.1</version>
</dependency>
and
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.19</version>
<configuration>
<parallel>classes</parallel>
<threadCount>10</threadCount>
<suiteXmlFiles>
<suiteXmlFile>src/test/resources/${suite}.xml</suiteXmlFile>
</suiteXmlFiles>
<workingDirectory>target/</workingDirectory>
</configuration>
</plugin>
But thread count still equals 1
Is there some way to add thread-count from Pom file??

Answer 1

You may need to remove thread-count from your suite definition in your XML file as it will override any -threadcount parameter that Maven Surefire is passing to TestNG (see Command Line Parameters under Running TestNG).
From local testing it appears that threadCount and suiteXmlFiles aren't compatible and from the Maven Surefire Plugin documentation for suiteXmlFiles is states:
Note that suiteXmlFiles is incompatible with several other parameters of this plugin, like includes/excludes.
I believe that threadCount is another of the incompatible "other parameters".
Some of the same options available in TestNG XML files are also available when configuring the Maven Surefire Plugin so it looks like you will have to "port" your TestNG XML to Maven Surefire Plugin Configuration XML.
In my local testing I found that I could simply omit suiteXmlFiles and the plugin found and ran my tests with the specified threadCount. Depending on your TestNG XML your solution might take a bit more work.

Answer 2

I dont try to do this, but this configuration should work.
I'm not sure, but to use this you should use surefire plugin with version 2.19+. Also I recommend to not use surefire-specific element names in section (like <parallel>, <threadCount>, <groups> etc) when you use TestNG. The better choose is to use <properties> section with set of <property> values. Those values will be passed to testNG command line. Behavior for such properties are clearly described in TestNG documentation
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.19</version>
<dependencies>
<dependency>
<groupId>org.apache.maven.surefire</groupId>
<artifactId>surefire-testng</artifactId>
<version>2.19</version>
</dependency>
</dependencies>
<configuration>
<suiteXmlFiles>
<suiteXmlFile>suites/my-suite.xml</suiteXmlFile>
</suiteXmlFiles>
<!-- DONT USE THIS
<parallel>methods</parallel>
<threadCount>5</threadCount>
-->
<properties>
<property>
<name>parallel</name>
<value>methods</value>
</property>
<property>
<name>threadcount</name>
<value>5</value>
</property>
<property>
<name>dataproviderthreadcount</name>
<value>3</value>
</property>
</properties>
</plugin>