Unambiguously determining the mass composition of ultra-high energy cosmic rays is a key challenge at the frontier of cosmic ray research. The mass composition is inferred from air shower observables using air shower simulations, which rely on hadronic interaction models. Current hadronic interaction models lead to varying interpretations, therefore tests of hadronic interaction models with air shower measurements are important. Such tests may even reveal new physics phenomena. Tests have been done by various experiments and cover the cosmic ray energies from PeV to tens of EeV. In this talk, the Working Group on Hadronic interactions and Shower Physics presents a summary of tests and measurements related to hadronic interactions in air showers from the Pierre Auger Observatory, Telescope Array, IceCube, KASCADE-Grande, EAS MSU, SUGAR and NEVOD-DECOR. Results include measurements of the proton-air cross-section, the lateral density profile of muons in air showers as well as electrons and photons, TeV muons, and the muon production depth. Our goal is to develop a consistent picture out of the individual measurements, to gain a detailed understanding where current hadronic interaction models succeed or fail in describing air shower observables.