Calling a shell command from Ruby hangs when running RSpec test

Question

The following scenarios produce the expected results:

from zsh, execute:

/usr/local/bin/pg_dump mydatabase  #=> a bunch of sql output

from irb or rails console, execute:

`/usr/local/bin/pg_dump my_database` #=> a bunch of sql output

Call the same shell command from within a method:

class AppDb
  def contents
    `/usr/local/bin/pg_dump my_database`
  end
end

# from rails console:
AppDb.new.contents #=> a bunch of sql stuff

However, when I test the very same AppDb class from Rspec, the shell command hangs indefinitely at the assertion:

expect(AppDb.new.contents).to match "PostgreSQL database dump complete"

Do you have any idea why this might be?

Probably you need to try this solution stackoverflow.com/questions/11349270/… — Alex Kojin
– Alex Kojin, Commented May 8, 2017 at 20:38
@AlexKojin thanks, the problem, however, is not with capturing stdout, that works fine. e.g. if I replace the pg_dump command with pwd, the result is properly captured and tested by rspec. The problem is that pg_dump is hanging (only in rspec context) and there's no diagnostic info available. — Les Nightingill
– Les Nightingill, Commented May 8, 2017 at 23:38

Les Nightingill · Accepted Answer · 2017-05-22 04:11:31Z

1

The hang is due to:

the rspec configuration in spec_helper.rb

config.use_transactional_fixtures = true

This initiates a postgresql BEGIN block, which initiates locking on the tables
in combination with the use of pg_dump, which cannot execute due to the database locks. It hangs (forever or for a specified timeout) waiting for the locks to be removed.

So the solution is simply to set use_transactional_fixtures to false. Of course, this leaves the database with test data at the end of the spec, which must be handled another way. DatabaseCleaner can be used, but not with transaction strategy, as this will have the same problem.

answered May 22, 2017 at 4:11

Les Nightingill

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