I've seen errors like this and here are some things to check:
Are you running a too old version of merlin?
Is your .merlin file calling ppx's correctly? (it's tricky but
jbuilder/dune does a good job with this).

On Fri, Jun 22, 2018 at 2:19 PM Paul A. Steckler <steck@stecksoft.com>
wrote:

> When using the Jane St inline testing framework, Merlin in Emacs
> complains about each "let%test" instance, citing "uninterpreted
> extension 'test'".
>
> Is there a way to make that warning disappear?
>
> -- Paul
>
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