ArtifactResolver vm = (ArtifactResolver) lookupMojo( getGoal(), new File( testRoot, "pom.xml" ) );
MavenProject project = new MavenProjectStub();
//addCompileSourceRoot will generate singletonList if null, which doesn't support a second add.
setVariableValueToObject( project, "compileSourceRoots", new ArrayList<String>() );
project.addCompileSourceRoot( new File( testRoot, "src/main/java" ).getAbsolutePath() );
//required field of mojo
setVariableValueToObject( vm, "project", project );
return vm;