The coronavirus disease (Covid-19) pandemic raised challenges for everyday life. Development of new diagnostic tests was necessary, but under such enormous pressure risking inadequate evaluation. Against a background of concern about standards applied to the evaluation of in vitro diagnostic tests (IVDs), clear statistical thinking was needed on the principles of diagnostic testing in general, and their application in a pandemic. Therefore, in July 2020, the Royal Statistical Society convened a Working Group of six biostatisticians to review the statistical evidence needed to ensure the performance of new tests, especially IVDs for infectious diseases—for regulators, decision-makers, and the public. The Working Group’s review was undertaken when the Covid-19 pandemic shone an unforgiving light on current processes for evaluating and regulating IVDs for infectious diseases. The report’s findings apply more broadly than to the pandemic and IVDs, to diagnostic test evaluations in general. A section of the report focussed on lessons learned during the pandemic and aimed to contribute to the UK Covid-19 Inquiry’s examination of the response to, and impact of, the Covid-19 pandemic to learn lessons for the future. The review made 22 recommendations on what matters for study design, transparency, and regulation.