I've already fixed this stuff in the following way:
I've added to pom.xml of mainProject
<plugin>
<artifactId>maven-war-plugin</artifactId>
<version>2.1.1</version>
<configuration>
<packagingIncludes>**/*.properties,**/*.class</packagingIncludes>
<attachClasses>true</attachClasses>
</configuration>
</plugin>
Then add dependency for projectForTesting:
<dependency>
<groupId>com.project.test</groupId>
<artifactId>mainProject</artifactId>
<version>${project.version}</version>
<classifier>classes</classifier>
</dependency>