When running `make installcheck` I get can not connect to database
If you're trying to build an extension on Ubuntu, you may have to set the port to isolate which version of PostgreSQL you wish to test the extension on with PGPORT. You can see here make install check is connecting on 5433 with the socket name .s.PGSQL.5432,

You likely want port 5432

make PGPORT=5433 installcheck