Verifying whether code meets its specifications requires critical thinking and analysis. However, cognitive biases may influence how well software engineers verify and test code. In this paper, we explore cognitive reflection and its association with accurately verifying code via both manual inspection and unit testing.

In a two-phase exploratory study of Software Engineering undergraduate students (n=140), we examined their performance on Cognitive Reflection Tests (CRT), manual verification of function implementations, and the accuracy of unit test suites. The first phase found no relationship between CRT and unit test accuracy. However, the higher a student’s CRT score, the more likely they were to reject a defective implementation when inspecting it manually (p<0.0001, 95% CI 1.56-4.50).

The second phase replicated the outcomes on an alternate version of the CRT and on a different unit test assignment, revealing a positive correlation between CRT and recognizing defects (ρ=0.478, p<0.01). We conclude that cognitive reflection is associated with software engineering students’ aptitude at identifying defects, but is not associated with their affirmation of algorithms without defects, nor with the accuracy of their unit tests.