It is necessary for the testing of AI systems prior to placing on the market or putting into service to be carried out, as appropriate, throughout the development process, with a view to anticipating and reducing potential risks and ensuring that those systems function as intended during actual use. AI systems should be tested under conditions that reflect real-world conditions and in line with up to date scientific and technical methodologies. The test data used to validate AI systems should be free from bias and appropriately represent the intended user population's diversity, where relevant. Those activities are particularly relevant with regard to high-risk AI systems, for which specific requirements regarding testing should be laid down in this Regulation.