Minitest: rake test:all fails while explicit testing does not - ruby-on-rails

Question

I have a weird problem which is bugging me for days now... and I don't have a single clue.
I have a rails 4 app which i test using Minitest and guard. So far everything went fine until at some point (which unfortunately I'm not able to reconstruct although I was using guard, maybe my collaborators introduced the issues...) some of our tests fail. The weird thing is: bundle exec rake test:all fails:
DEPRECATION WARNING: rake test:all is deprecated and will be removed in Rails 5. Use rake test to run all tests in test directory. (called from mon_synchronize at /usr/lib/ruby/2.3.0/monitor.rb:214)
# Running tests with run options --seed 53809:
WARNING: The next major version of capybara-webkit will require at least version 5.0 of Qt. You're using version 4.8.7.
............EE....EE.............F..
Finished tests in 26.018707s, 1.3836 tests/s, 1.6142 assertions/s.
Error:
PlaceTest#test_return_''_if_too_many_characters_to_translate:
NoMethodError: undefined method `failsafe_translate' for nil:NilClass
test/models/place_auto_translation_test.rb:29:in `block in <class:PlaceTest>'
Error:
PlaceTest#test_test_places_are_valid:
NoMethodError: undefined method `geocode' for nil:NilClass
test/models/place_geocode_test.rb:21:in `block in <class:PlaceTest>'
Error:
PlaceTest#test_should_translate_text_below_character_limit:
NoMethodError: undefined method `failsafe_translate' for nil:NilClass
test/models/place_auto_translation_test.rb:34:in `block in <class:PlaceTest>'
Error:
PlaceTest#test_can_translate_if_valid_credentials_given:
NoMethodError: undefined method `bing_translator' for nil:NilClass
test/models/place_auto_translation_test.rb:16:in `block in <class:PlaceTest>'
Failure:
Index page Feature Test#test_0002_language is switched to german [/home/blubber/software_projects/rails/workspace/lberg-map/test/features/index_page_test.rb:16]
Minitest::Assertion: Expected to include "Neuer Ort".
36 tests, 42 assertions, 1 failures, 4 errors, 0 skips
Now, while trying to understand the issues raised I was testing the problematic files individually (within my editor and guard or on the command-line, same thing of course) it turns out, that there is actually no problem at all, all tests pass oO. Hence bundle exec rake test test/models/place_auto_translation_test.rb returns
# Running tests with run options --seed 55164:
.....
Finished tests in 25.472545s, 0.1963 tests/s, 0.2355 assertions/s.
5 tests, 6 assertions, 0 failures, 0 errors, 0 skips
Same goes for place_geocode_test.rb as well as the "failing" feature test. Any idea on what's happening here? The test file test/models/place_auto_translation_test.rb looks like this:
require_relative '../test_helper'
class PlaceTest < ActiveSupport::TestCase
def setup
#valid_translator = BingTranslatorWrapper.new(ENV['bing_id'], ENV['bing_secret'], ENV['microsoft_account_key'])
#place = Place.new(name: 'Kiezspinne',
street: 'Schulze-Boysen-Straße',
house_number: '13',
postal_code: '10365',
city: 'Berlin',
description_en: 'This is a test')
end
# AUTO TRANSLATION WRAPPER TESTS
test 'can translate if valid credentials given' do
assert_not_nil #valid_translator.bing_translator
end
test 'cannot translate if API id and key invalid or no microsoft account key' do
invalid_translator = BingTranslatorWrapper.new(ENV['wrong_id'], ENV['wrong_secret'], ENV['microsoft_account_key'])
assert_nil invalid_translator.bing_translator
invalid_translator = BingTranslatorWrapper.new(ENV['bing_id'], ENV['bing_secret'], ENV['wrong_microsoft_account_key'])
assert_equal '', invalid_translator.failsafe_translate('Dies ist ein Test', 'en', 'de')
end
test "return '' if too many characters to translate" do
text = '13 characters' * 1000
assert_equal '', #valid_translator.failsafe_translate(text, 'en', 'de')
end
test 'should translate text below character limit' do
text = 'This is a test'
assert_equal 'Automatische Übersetzung: Dies ist ein Test', #valid_translator.failsafe_translate(text, 'en', 'de')
end
test 'should autotranslate after_create' do
#place.save
#place.reload
assert_equal "Automatische Übersetzung: Dies ist ein Test", #place.description_de
end
end
and test_helper.rb looks like this
ENV['RAILS_ENV'] ||= 'test'
require File.expand_path('../../config/environment', __FILE__)
require 'rails/test_help'
require 'minitest/rails'
require 'minitest/reporters'
require 'minitest/rails/capybara'
reporter_options = { color: true }
Minitest::Reporters.use!(
Minitest::Reporters::DefaultReporter.new(reporter_options),
ENV,
Minitest.backtrace_filter
)
class ActiveSupport::TestCase
# Setup all fixtures in test/fixtures/*.yml for all tests in alphabetical order.
fixtures :all
end
Geocoder.configure(:lookup => :test)
Geocoder::Lookup::Test.set_default_stub(
[
{
'latitude' => 52,
'longitude' => 12,
'address' => {
'road' => 'Magdalenenstr.',
'house_number' => '19',
'postcode' => '10365',
'town' => 'Berlin',
},
'type' => 'house',
}
]
)
# allow tile loading from foreign server
Capybara::Webkit.configure do |config|
%w[a b c].each { |x| config.allow_url("tile-#{x}.openstreetmap.fr") }
end
# While testing with Javascript flag, test runs in another thread,
# thus created fixtures are not available without the following setup
class Capybara::Rails::TestCase
self.use_transactional_fixtures = false
before do
if metadata[:js]
Capybara.javascript_driver = :webkit
Capybara.current_driver = Capybara.javascript_driver
DatabaseCleaner.strategy = :truncation
DatabaseCleaner.start
end
end
after do
if metadata[:js]
DatabaseCleaner.clean
end
Capybara.reset_sessions!
Capybara.current_driver = Capybara.default_driver
end
end
Thanks a thousand, best
Andi