Set different java language level between source code and test in the lastest stable version of Idea?

Actually, I configured the Maven pom as followed:

    <plugin>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>3.1</version>
        <configuration>
            <source>1.6</source>
            <target>1.6</target>
            <testSource>8</testSource>
            <testTarget>8</testTarget>
        </configuration>
    </plugin>

But it doesn't work for Idea, How should I do to solve this?