  Traditionally, energy efficiency research has focused on reducing energy
consumption at the hardware level and, more recently, in the design and coding
phases of the software development life cycle. However, software testing's
impact on energy consumption did not receive attention from the research
community. Specifically, how test code design quality and test smell (e.g.,
sub-optimal design and bad practices in test code) impact energy consumption
has not been investigated yet. This study examined 12 Apache projects to
analyze the association between test smell and its effects on energy
consumption in software testing. We conducted a mixed-method empirical analysis
from two dimensions; software (data mining in Apache projects) and developers'
views (a survey of 62 software practitioners). Our findings show that: 1) test
smell is associated with energy consumption in software testing. Specifically
smelly part of a test case consumes 10.92\% more energy compared to the
non-smelly part. 2) certain test smells are more energy-hungry than others, 3)
refactored test cases tend to consume less energy than their smelly
counterparts, and 4) most developers lack knowledge about test smells' impact
on energy consumption. We conclude the paper with several observations that can
direct future research and developments.
