Shares in online grocer Ocado OCDO.L were up 1.5%, while market leader Tesco's TSCO.L shares were down 0.5% on negative read-across. By Joice Alves Aug 19 (Reuters) - London's FTSE 100 .FTSE was largely unchanged in thin summer trading on Wednesday, hardly reacting to a surprise rise in domestic inflation last month and the British government's plan to ramp up COVID-19 testing. Health minister Matt Hancock said Britain is planning to bring in population-wide mass testing for coronavirus to help control the pandemic, adding that the government is working with London's Heathrow Airport to shorten quarantine.