The summary is that it ignores one file in favor of the other.
    util.concurrent, like nearly all our packages, has two .gwt.xml files: one
    for prod and one for tests. However, unlike our other packages, as of this
    writing it has test supersource but no prod supersource.

    GWT happens to use the prod .gwt.xml, so it looks for no supersource for
    tests, either. This causes it to fail to find AtomicLongMapTest.

      </releases>
    </repository>
  </repositories>

  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.its.plugins</groupId>
        <artifactId>maven-it-plugin-log-file</artifactId>
        <version>2.1-SNAPSHOT</version>
        <executions>
          <execution>
            <id>equal-build-exec-id</id>
            <phase>initialize</phase>
            <goals>

          <description>
            A set of dependencies which the plugin requires in order to function. This enables the plugin to function
            independently of its POM (or at least to declare the libraries it needs to run).
          </description>
        </field>
      </fields>
      <codeSegments>
        <codeSegment>
          <version>2.0.0+</version>
          <code><![CDATA[

      <plugin>
        <artifactId>maven-source-plugin</artifactId>
        <configuration>
          <excludes>
            <!-- 3. Don't include it in the source jar (since it's really more of a "test" than it is production code). -->
            <exclude>**/ForceGuavaCompilation*</exclude>
            <exclude>**/DummyJavadocClass*</exclude>
          </excludes>
        </configuration>
      </plugin>
      <plugin>

  <!-- mirrors
   | This is a list of mirrors to be used in downloading artifacts from remote repositories.
   |
   | It works like this: a POM may declare a repository to use in resolving certain artifacts.
   | However, this repository may have problems with heavy traffic at times, so people have mirrored
   | it to several places.
   |
   | That repository definition will have a unique id, so we can create a mirror reference for that

      <snapshots/>
      <releases/>
    </repository>
  </repositories>

  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.its.plugins</groupId>
        <artifactId>maven-it-plugin-log-file</artifactId>
        <version>2.1-SNAPSHOT</version>
        <executions>
          <execution>
            <id>equal-build-exec-id</id>
            <phase>initialize</phase>
            <goals/>

  <artifactId>parent</artifactId>
  <version>1.0-SNAPSHOT</version>
  <dependencies>
    <dependency>
      <groupId>org.apache.maven.its</groupId>
      <artifactId>maven-core-it-support</artifactId>
      <version>1.3</version>
      <scope>runtime</scope>
      <exclusions>
        <exclusion>
          <groupId>commons-lang</groupId>
          <artifactId>commons-lang</artifactId>

  </distributionManagement>

  <properties>
    <maven.site.path>ref/4-LATEST/${project.artifactId}</maven.site.path>
  </properties>

  <dependencyManagement>
    <!-- Not included:
         - apache-maven, as it delivers the binaries
         - maven-compat, only used by apache-maven distributions to support older releases
         - maven-slf4j-provider, only used by apache-maven distributions

    <!-- javax.inject (JSR-330) -->
    <exportedPackage>javax.inject.*</exportedPackage>
    <!-- javax.enterprise.inject (JSR-299): Must never be exported if needed at plugin level, plugin adds it
         there is no justification to get it at Maven level and leaking it will conflict.
    <exportedPackage>javax.enterprise.util.*</exportedPackage>
    <exportedPackage>javax.enterprise.inject.*</exportedPackage>
    -->

						</goals>
					</execution>
				</executions>
				<configuration>
					<failOnError>false</failOnError>
					<ignored>
						<difference>
							<!-- seems to be a clirr bug that it cannot handle the different inherited 
								return types -->
							<className>**</className>
							<differenceType>7006</differenceType>
							<method>*</method>
							<from>*</from>
							<to>*</to>