This seems to work:
@Test
public void test() {
// original components
JTable jTable = new JTable();
JScrollPane scrollPane = new JScrollPane(jTable);
// add them to tab
JTabbedPane jTabbedPane = new JTabbedPane();
jTabbedPane.addTab("tab1", scrollPane);
jTabbedPane.setSelectedComponent(scrollPane);
// get them out of selected tab
JScrollPane scrollRef = (JScrollPane) jTabbedPane.getSelectedComponent();
JTable tableRef = (JTable) scrollRef.getViewport().getComponents()[0];
assertTrue(tableRef == jTable);
}