question: public void testCommonPrefix ( ) { String returned = m_Trie . getCommonPrefix ( ) ; assertEquals ( "Common prefixes differ" , 0 , returned . length ( ) ) ; String expected = "this is a" ; Trie t = buildTrie ( new String [ ] { m_Data [ 0 ] , m_Data [ 1 ] } ) ; returned = t . getCommonPrefix ( ) ; assertEquals ( "Common prefixes differ" , expected . length ( ) , returned . length ( ) ) ; }
target:  tests whether the common prefix is determined correctly