Twitter has announced a test project allowing tweets to be expanded to 280 characters, double the existing limit in the latest effort to boost flagging growth at the social network. <br/><br/>San Francisco-based Twitter said the new limit, a major shift for the messaging platform known for its 140-character tweets, aims to address a major cause of frustration for many users. <br/><br/>Twitter chief executive Jack Dorsey said this is a small change, but a big move for them. <br/><br/>Twitter, which became a public company in 2013, has never reported a profit even though it has built a loyal base of celebrities, journalists and political figures.