I recommend using type instead of classifier (see also: classifier). It tells Maven a bit more explicitly what you are doing (and I’ve found that m2eclipse and q4e both like it better).
<dependency>
<groupId>com.myco.app</groupId>
<artifactId>foo</artifactId>
<version>1.0-SNAPSHOT</version>
<type>test-jar</type>
<scope>test</scope>
</dependency>