  Context. White-box test generation is a technique used for automatically
selecting test inputs using only the source or binary code. However, such
techniques encounter challenges when applying them to complex programs. One of
the main challenges is handling the dependencies of the unit under test.
  Objective. Without proper actions, generated tests cannot cover all parts of
the source code, or calling the dependencies may cause unexpected side effects
(e.g., file system or network access). These issues should be tackled while
maintaining the advantages of white-box test generation.
  Method. In this paper, we present an automated source code transformation
approach tackling the dependency issue for white-box test generation. This
technique isolates the test execution by creating a parameterized sandbox
wrapped around the transformed unit. We implemented the approach in a
ready-to-use tool using Microsoft Pex as a test generator, and evaluated it on
10 open-source projects from GitHub having more than 38.000 lines of code in
total.
  Results. The results from the evaluation indicate that if the lack of
isolation hinders white-box test generation, then our approach is able to help:
it increases the code coverage reached by the automatically generated test,
while it reduces unwanted side effects. Also, our results act as a unique
baseline for the test generation performance of Microsoft Pex on open-source
projects.
  Conclusion. Based on the results, our source code transformations might serve
well for alleviating the isolation problem in white-box test generation as it
increases the coverage reached in such situations, while maintaining the
practical applicability of the tests generated on the isolated code.
