A typical HPC facility supports hundreds of applications that are supported by the HPC team. Building these software packages is a challenge and then figuring out how this software stack behaves due to system changes (OS release, kernel path, glibc, etc…).
Application Testing is difficult. The commercial and open-source application typically provide test scripts such as make test or ctest that can test the software after building (make) step. Unfortunately, these methods perform tests prior to installation so the ability to test software in production is not possible. One could try to change the vendor test script to the install path but this requires significant change into a complex makefile
Writing test scripts manually can be tedious, also there is no sharing of tests and most likely they are not compatible to work with other HPC sites because of different software stack and hardcoded paths specific to the site. Easybuild takes a step at improving application build process by automating the entire software workflow that can be built on any HPC site.
Buildtest takes a similar approach as EasyBuild but focusing on application testing.