I have installed postgres and postgis as described here
brew install postgres
brew install postgis
createdb postgis_test
psql postgis_test
psql (9.6.2)
Type "help" for help.
postgis_test=# CREATE EXTENSION postgis;
ERROR: could not open extension control file "/usr/local/share/postgresql/extension/postgis.control": No such file or directory
ERROR: could not stat file "/usr/local/share/postgresql/extension/postgis--2.3.2.sql": No such file or directory
ERROR: could not access file "$libdir/postgis-2.3": No such file or directory
What might be the error ? and how to solve it ?