Large simulation efforts are required to provide synthetic galaxy catalogs
for ongoing and upcoming cosmology surveys. These extragalactic catalogs are
being used for many diverse purposes covering a wide range of scientific
topics. In order to be useful, they must offer realistically complex
information about the galaxies they contain. Hence, it is critical to implement
a rigorous validation procedure that ensures that the simulated galaxy
properties faithfully capture observations and delivers an assessment of the
level of realism attained by the catalog. We present here a suite of validation
tests that have been developed by the Rubin Observatory Legacy Survey of Space
and Time (LSST) Dark Energy Science Collaboration (DESC). We discuss how the
inclusion of each test is driven by the scientific targets for static
ground-based dark energy science and by the availability of suitable validation
data. The validation criteria that are used to assess the performance of a
catalog are flexible and depend on the science goals. We illustrate the utility
of this suite by showing examples for the validation of cosmoDC2, the
extragalactic catalog recently released for the LSST DESC second Data
Challenge.
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