Testing is an indispensable part of software development efforts. It helps to improve the quality of software systems by finding bugs and errors during development and deployment. Huge amount of resources are spent on testing efforts. However, to what extent are they used in practice? In this study, we investigate the adoption of testing in open source projects. We study more than 20,000 non-trivial software projects and explore the correlation of test cases with various project development characteristics including: project size, development team size, number of bugs, number of bug reporters, and the programming languages of these projects.