spawn does not support the < direction but you can do like this:
spawn sh -c "mysql -u root -h localhost -proot dbTest < temp.sql"
Seems like you want to run mysql in the non-interactive way so you can also use Expect's system command:
system "mysql -u root -h localhost -proot dbTest < temp.sql"
or Tcl's exec command:
exec mysql -u root -h localhost -proot dbTest < temp.sql >@ stdout 2>@ stderr
You may need to put the whole system or exec command in a catch block in case the mysql fails:
catch {system "mysql ..."} catched
# or
catch {exec mysql ...} catched