Building Performance Simulation (BPS), a useful tool to assess the operational performance of buildings and systems, can often be computationally expensive. The use of BPS is cumbersome for problems where the speed of response is important, e.g. real-time control, uncertainty quantification, parametric exploration, or stock modelling. Emulators, such as those based on regression, offer a faster substitute, but their reliability can be questionable. This paper proposes seven tests to check if an emulator is a suitable replacement for simulation in practice. The tests are categorized using four criteria: accuracy, speed, generalisability, and ease of use. The tests can be included in the process of setting up an emulator-based workflow. A use case is provided for emulators based on linear and non-linear regression (Gaussian Process models). This work aims to enable a practitioner to reliably conduct performance assessment for buildings using emulators.