Concurrent programming can be notoriously complex and error-prone. Programming bugs can arise from a variety of sources, such as operation re-reordering, or incomplete understanding of the memory model. A variety of formal and model checking methods have been developed to address this fundamental difficulty. While technically interesting, existing academic methods are still hard to apply to the large codebases typical of industrial deployments, which limits their practical impact. This paper presents Lincheck – a new practical tool for testing concurrent algorithms implemented in JVM-based languages, such as Java, Kotlin, or Scala. Roughly, Lincheck takes the list of operations on the data structure to be tested, generates a series of concurrent scenarios, executes them in either stress testing or model checking mode, and checks whether there exists some sequential execution which can explain the results.