The adoption of agile approaches has put an increased emphasis on testing,resulting in extensive test suites. These suites include a large number of tests, in whichdevelopers embed knowledge about meaningful input data and expected properties as oracles.This article surveys works that exploit this knowledge to enhance manually written tests withrespect to an engineering goal (e.g., improve coverage or refine fault localization). While theseworks rely on various techniques and address various goals, we believe they form an emergingand coherent field of research, which we coin “test amplification”. We devised a first set ofpapers from DBLP, searching for all papers containing "test" and "amplification" in theirtitle. We reviewed the 70 papers in this set and selected the 4 papers that fit the definitionof test amplification. We use them as the seeds for our snowballing study, and systematicallyfollowed the citation graph. This study is the first that draws a comprehensive picture of thedifferent engineering goals proposed in the literature for test amplification. We believe thatthis survey will help researchers and practitioners entering this new field to understand morequickly and more deeply the intuitions, concepts and techniques used for test amplification.