Since the emergence of SARS-CoV-2, many diagnostic tests including molecular and serological assays have been developed and approved by the Food and Drug Administration (FDA) for diagnosis of Covid-19. However, concerns about the sensitivity and specificity of many diagnostic assays, especially the rapid tests, have been raised. Diagnostic tests with unacceptable rates of false positive and false negative results interferes with therapeutic management of patients and can bring serious implications for public health authorities in the decision-making process regarding Covid-19 control. In this context, understanding key concepts in terms of development and validation of diagnostic assays is crucial for correct interpretation of test results. The parameters for validating diagnostic tests include analytical sensitivity, analytical specificity, clinical sensitivity, clinical specificity, positive likelihood ratio, negative likelihood ratio, positive predictive value (PPV), negative predictive value (NPV), repeatability, reproducibility, and accuracy (Table 1). After initial development and optimization of a new Covid-19 test, the performance of the assay should be assessed using a set of well-defined clinical samples taking into account the required sample size. Ideally, data used for validation of Covid-19 test should be published in a peer-reviewed publication to allow independent evaluation.