 Tester made his first stage appearance at the age of 11, in "The Merry Wives of Windsor", 1930, receiving positive reviews from London; he also appeared as Emil in "Emil and the Detectives".From 1934 he became better known as a child actor in film in his native Britain.Tester's characters often met with doomed fates, in such early films as Carol Reed's "Midshipman Easy" (1935), "Tudor Rose" (1936), Robert Stevenson's "Non-Stop New York" (1937), "The Stars Look Down" (1939) and "Sabotage".