It Will Never Work in Theory

When, How, and Why Developers (Do Not) Test in Their IDEs

Posted Jun 8, 2016 by Greg Wilson

| Testing |

Moritz Beller, Georgios Gousios, Annibale Pannichella, and Andy Zaidman: "When, How, and Why Developers (Do Not) Test in Their IDEs". ESEC/FSE'15, August 2015,,

We report on the surprising results of a large-scale field study with 416 software engineers whose development activity we closely monitored over the course of five months, resulting in over 13 years of recorded work time in their integrated development environments (IDEs). Our findings question several commonly shared assumptions and beliefs about testing and might be contributing factors to the observed bug proneness of software in practice: the majority of developers in our study does not test; developers rarely run their tests in the IDE; Test-Driven Development (TDD) is not widely practiced; and, last but not least, software developers only spend a quarter of their work time engineering tests, whereas they think they test half of their time.

The bullet point summary is fairly innocuous:

  • The majority of projects and users do not practice testing actively.
  • Developers largely do not run tests in the IDE. However, when they do, they do it heftily.
  • Tests and production code do not co-evolve gracefully.
  • Tests run in the IDE take a very short amount of time.
  • Developers frequently select a specific set of tests to run in the IDE. In most cases, developers execute one test.
  • Most test executions in the IDE fail.
  • The typical immediate reaction to a failing test is to dive into the offending production code.
  • TDD is not widely practiced. Programmers who claim to do it, neither follow it strictly nor for all their modifications.
  • Developers spend a quarter of their time engineering tests in the IDE. They overestimated this number twofold.

but the details are rather depressing. For example, in 85% of development sessions, no tests were run, even in those projects that had unit tests. Similarly, developers do test their changes to production code, but the correlation coefficient is pretty weak (0.38), and the correlation between test and production code co-evolving is even weaker (0.35). Fast tests don't correlate with more frequent test execution, and only 4% of sessions that had test execution followed the classic red-green-refactor TDD cycle. It's possible—indeed, likely—that the researchers' IDE instrumentation missed some things, but it's painfully clear that we still have a long way to go when it comes to real-world adoption of better testing practices.

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