How are non-conflicting configurations resolved if multiple profiles are activated? - maven

Question

Following up this question:
I can't find information on how the union of multiple (active) maven profiles is built, under the condition that they are not conflicting.
Consider the following example:
I want to control how my test cases are run with maven-surefire-plugin. First I need to configure two different environments (jenkins-CI-server) and local. Second I want to enable running different sets of tests.
I would have four profiles:
env_jenkins for running on jenkins
env_local for running on local
testset_A for running some tests
testset_B for running some other tests
Note that for all those profiles I need to define the plugin configuration for the maven-surefire-plugin.
(See below for the concrete xml-configuration)
Then I would like to combine the profiles to run - for example - testset A on jenkins.
My questions:
Is such a behaviour supported by maven?
On which stage does the overriding mentioned in the related question occur? Is the entire plugin configuration overridden (-> my example would not work). Or only really conflicting parts (-> my example would work)?
Does the overriding behaviour depend on the plugin or is it consistent among all maven plugins?
Example pom:
<profiles>
<!-- handle system configurations (e.g. one for jenkins environment, one for local) -->
<profile>
<id>env_jenkins</id>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<configuration>
<systemPropertyVariables>
<arquillian.launch>jbossas-managed</arquillian.launch>
<jbossHttpPortOverride>8080</jbossHttpPortOverride>
</systemPropertyVariables>
</configuration>
</plugin>
</plugins>
</build>
</profile>
<profile>
<id>env_local</id>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<configuration>
<systemPropertyVariables>
<arquillian.launch>jbossas-managed-jenkins</arquillian.launch>
<jbossHttpPortOverride>${jboss.http.port}</jbossHttpPortOverride>
</systemPropertyVariables>
</configuration>
</plugin>
</plugins>
</build>
</profile>
<!-- define different test sets -->
<profile>
<id>testset_A</id>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<configuration>
<includes>
<include>TestA1.java</include>
<include>TestA2.java</include>
<include>TestA3.java</include>
</includes>
</configuration>
</plugin>
</plugins>
</build>
</profile>
<profile>
<id>testset_B</id>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<configuration>
<includes>
<include>TestB1.java</include>
</includes>
</configuration>
</plugin>
</plugins>
</build>
</profile>
</profiles>

Answer 1

It works using the same inheritance/merging process that works between parent and children POMs. Using the Maven help plugin can confirm this (using Maven 3.3.9):
Order of profile declarations in the POM matters. A plugin configuration inherits the same plugin's configuration declared in an active profile appearing before it in the POM.
The attributes combine.self and combine.children can be used to control the merging.
Example with default settings (without using combine.self or combine.children, i.e. with combine.children="merge" implicitly):
mvn help:effective-pom -Penv_local,testset_A
Effective POM shows merged configurations:
...
<plugin>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.12.4</version>
<executions>
<execution>
<id>default-test</id>
<phase>test</phase>
<goals>
<goal>test</goal>
</goals>
<configuration>
<includes>
<include>TestA1.java</include>
<include>TestA2.java</include>
<include>TestA3.java</include>
</includes>
<systemPropertyVariables>
<arquillian.launch>jbossas-managed-jenkins</arquillian.launch>
<jbossHttpPortOverride>${jboss.http.port}</jbossHttpPortOverride>
</systemPropertyVariables>
</configuration>
</execution>
</executions>
<configuration>
<includes>
<include>TestA1.java</include>
<include>TestA2.java</include>
<include>TestA3.java</include>
</includes>
<systemPropertyVariables>
<arquillian.launch>jbossas-managed-jenkins</arquillian.launch>
<jbossHttpPortOverride>${jboss.http.port}</jbossHttpPortOverride>
</systemPropertyVariables>
</configuration>
</plugin>
...
Example with combine.self="override":
<profile>
<id>testset_A</id>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<configuration combine.self="override">
<includes>
<include>TestA1.java</include>
<include>TestA2.java</include>
<include>TestA3.java</include>
</includes>
</configuration>
</plugin>
</plugins>
</build>
</profile>
mvn help:effective-pom -Penv_local,testset_A
Effective POM shows only testset_A's configuration:
<plugin>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.12.4</version>
<executions>
<execution>
<id>default-test</id>
<phase>test</phase>
<goals>
<goal>test</goal>
</goals>
<configuration combine.self="override">
<includes>
<include>TestA1.java</include>
<include>TestA2.java</include>
<include>TestA3.java</include>
</includes>
</configuration>
</execution>
</executions>
<configuration combine.self="override">
<includes>
<include>TestA1.java</include>
<include>TestA2.java</include>
<include>TestA3.java</include>
</includes>
</configuration>
</plugin>
Example with combine.children="append":
<profile>
<id>testset_A</id>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<configuration combine.children="append">
<includes>
<include>TestA1.java</include>
<include>TestA2.java</include>
<include>TestA3.java</include>
</includes>
</configuration>
</plugin>
</plugins>
</build>
</profile>
mvn help:effective-pom -Penv_local,testset_A
Effective POM shows merged configurations. In this case, it happens to be the same as the first example. However, had testset_A introduced configuration XML elements that already exist in env_local, they would have been appended:
<plugin>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.12.4</version>
<executions>
<execution>
<id>default-test</id>
<phase>test</phase>
<goals>
<goal>test</goal>
</goals>
<configuration combine.children="append">
<systemPropertyVariables>
<arquillian.launch>jbossas-managed-jenkins</arquillian.launch>
<jbossHttpPortOverride>${jboss.http.port}</jbossHttpPortOverride>
</systemPropertyVariables>
<includes>
<include>TestA1.java</include>
<include>TestA2.java</include>
<include>TestA3.java</include>
</includes>
</configuration>
</execution>
</executions>
<configuration combine.children="append">
<systemPropertyVariables>
<arquillian.launch>jbossas-managed-jenkins</arquillian.launch>
<jbossHttpPortOverride>${jboss.http.port}</jbossHttpPortOverride>
</systemPropertyVariables>
<includes>
<include>TestA1.java</include>
<include>TestA2.java</include>
<include>TestA3.java</include>
</includes>
</configuration>
</plugin>