We'll respond shortly.
We keep getting this error across multiple projects & machines, with different versions of the pg gem and the PostgreSQL server, with varying consistency. Switching the tests to sqlite seems to fix it.
Failure/Error: Unable to find matching line from backtrace ActiveRecord::StatementInvalid: NoMethodError: undefined method `fields' for nil:NilClass: SELECT "locations".* FROM "locations" WHERE "locations"."id" IN (11, 10, 5, 4, 1, 3, 2)
It appears that PG::Connection#async_exec is returning nil for some queries.
It was suggested to add a "fields" method for the nil class.
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If you want to test your media query css as part of your acceptance suite, you can just ask Capybara to resize the firefox window.
Don't use the iframe to do this, because it will be buggy. Note you will need to use min/max-width not min/max-device-width when defining your media queries. Otherwise resizing the browser window will not trigger the media query.
Capybara.current_session.driver.browser.manage.window.position = Struct.new(:x, :y).new(session_name == :default ? 0 : width, 0)
Thanks to Ryan for the tip.