Silence output to stdout during cli specs (#25211)

spec/rails_helper.rb

@@ -62,6 +62,10 @@ RSpec.configure do |config|
   config.infer_spec_type_from_file_location!
   config.filter_rails_from_backtrace!
 
+  config.define_derived_metadata(file_path: Regexp.new('spec/lib/mastodon/cli')) do |metadata|
+    metadata[:type] = :cli
+  end
+
   config.include Devise::Test::ControllerHelpers, type: :controller
   config.include Devise::Test::ControllerHelpers, type: :helper
   config.include Devise::Test::ControllerHelpers, type: :view
@@ -73,6 +77,10 @@ RSpec.configure do |config|
   config.include Redisable
   config.include SignedRequestHelpers, type: :request
 
+  config.before :each, type: :cli do
+    stub_stdout
+  end
+
   config.before :each, type: :feature do
     https = ENV['LOCAL_HTTPS'] == 'true'
     Capybara.app_host = "http#{https ? 's' : ''}://#{ENV.fetch('LOCAL_DOMAIN')}"
@@ -106,6 +114,10 @@ def attachment_fixture(name)
   Rails.root.join('spec', 'fixtures', 'files', name).open
 end
 
+def stub_stdout
+  allow($stdout).to receive(:write)
+end
+
 def stub_jsonld_contexts!
   stub_request(:get, 'https://www.w3.org/ns/activitystreams').to_return(request_fixture('json-ld.activitystreams.txt'))
   stub_request(:get, 'https://w3id.org/identity/v1').to_return(request_fixture('json-ld.identity.txt'))