Requiring HCV drug resistance testing prior to initial therapy is not currently advised. Dr. Freeman recently linked a study that covered some of the reasons – nicely summed up in the last paragraph below.

http://fixhepc.com/forum/resistance/1273-highly-detailed-article-on-daa-resistance.html
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Resistance Testing Before First-Line Therapy

There are many conditions for broad use of HCV resistance tests in clinical practice.

First, a standardized assay should be available as a purchasable kit, externally validated for its performance, and easy to use routinely in any virology laboratory with experience in molecular biology. Whatever the technology used, the assay should reliably report the presence of RASs with a validated and repeatable sensitivity of 15%, equivalent to population sequencing.

Second, interpretation and reporting of HCV resistance data should be homogenized and standardized through recommendations by an international organization.

Thirdly, clinically relevant RASs should be clearly identified, and only these should be reported and used for treatment decisions.

Finally, guidelines should be provided by international societies for treatment decisions based on results of drug resistance tests. The guidelines should be based on data from clinical trials and real-life studies that reported strong predictive values of the different RAS profiles.

Because none of these conditions have yet been met, systematic testing for HCV resistance before treatment should not be recommended. Systematic testing would seriously limit access to care and lead to erroneous decisions for a number of cases. Instead, treatment can be optimized for groups of patients known to have specific RASs in NS5A that reduce response to therapy.

http://freepdfhosting.com/b3d39c5e48.pdf
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The authors do reference the current exception for Merck’s Zepatier (elbasvir + grazoprevir) where pre-treatment NS5A resistance testing is prescribed to determine length of therapy and/or the addition of ribavirin for patients with GT1a (detail linked below).

http://www.natap.org/2016/HCV/020516_07.htm

Aside from this exception – the AASLD guidelines also recommend against resistance testing prior to initial therapy. Guidelines for retreatment – should initial therapies fail – are less concise.

J