Bug 183918 get relative file path of linkage library
model/org.eclipse.birt.report.model.tests/test/org/eclipse/birt/report/model/library/DesignLoadLibraryTest.java
assertTrue( dataSet3.getRoot( ) instanceof ReportDesignHandle );
		
		dataSet3.setDataSource( "LibA.dataSource1" ); 
		assertEquals( "LibA.dataSource1", dataSet3 
				.getProperty( SimpleDataSet.DATA_SOURCE_PROP ) );
		assertNotNull( dataSet3.getDataSource( ) );
		
		dataSet3.setDataSource( "dataSource1" ); 
		assertEquals( dataSource1, dataSet3.getDataSource( ) );
		
		designHandle.getCommandStack( ).undo( );
		assertEquals( "LibA.dataSource1", dataSet3 
				.getProperty( SimpleDataSet.DATA_SOURCE_PROP ) );
		assertNotNull( dataSet3.getDataSource( ) );
		
		designHandle.getCommandStack( ).undo( );
		assertEquals( dataSource1, dataSet3.getDataSource( ) );
		
		designHandle.getCommandStack( ).redo( );
		assertEquals( "LibA.dataSource1", dataSet3 
				.getProperty( SimpleDataSet.DATA_SOURCE_PROP ) );
		assertNotNull( dataSet3.getDataSource( ) );
		
		designHandle.getCommandStack( ).redo( );
		assertEquals( dataSource1, dataSet3.getDataSource( ) );
	}
	/**
	 * Tests the direct reference to data set.
	 * 
	 * @throws Exception