Cannot nest 'projectname/src/main/java' inside 'projectname/src'. To enable the nesting exclude 'main/' from 'projectname/src' in eclipse maven project

I noticed following error in my project in eclipse.

       
Cannot nest 'projectname/src/main/java' inside 'projectname/src'. To enable the nesting exclude 'main/' from 'projectname/src'

due to this error also my test of junit was not working. and problem was due to reason that i changed eclipse java project into maven project and in the pom file eclipse added

 <sourceDirectory>src</sourceDirectory>

 and due to this maven plugin was giving error after removing this line plugin error gone and also junit test were fine.