UQTestFuns is an open-source Python3 library of test functions commonly used within the applied uncertainty quantification (UQ) community. Specifically, the package provides: an implementation with minimal dependencies (i.e., NumPy and SciPy) and a common interface of many test functions a single entry point collecting test functions and their probabilistic input specifications in a single Python package an opportunity for an open-source contribution, supporting the implementation of new test functions or posting reference results. In short, UQTestFuns is an homage to the Virtual Library of Simulation Experiments (VLSE). v0.4.0 includes five additional test functions used in the context of reliability analysis (rare-events estimation) and metamodeling. The package is now tested against Python v3.11. The new version also includes several refactoring and update to the documentation.