We know some benefit criterion in articles such as:
C. H. Li, On isomorphisms of finite Cayley graphs-a survey, Discrete Math., 256 (2002) 301-334.
C. H. Li, Z. P. Lu, P. P. Pa'lfy, Further restrictions on the structure of finite CI-groups, J. Algebraic Combin., 26 (2007) 161-181.
Now, do you know which finite groups of order less than 100 are CI-groups?
For example, which groups of order 30 are CI-groups?