Enable the RSpec/ExpectOutput cop

Signed-off-by: Rémy Coutable <remy@rymai.me>

.rubocop.yml

@@ -987,6 +987,9 @@ RSpec/ExampleWording:
 RSpec/ExpectActual:
   Enabled: true
+RSpec/ExpectOutput:
+  Enabled: true
+
 # Checks the file and folder naming of the spec file.
 RSpec/FilePath:
   Enabled: true

.rubocop_todo.yml

@@ -23,10 +23,6 @@ RSpec/EmptyLineAfterFinalLet:
 RSpec/EmptyLineAfterSubject:
   Enabled: false
-# Offense count: 3
-RSpec/ExpectOutput:
-  Enabled: false
-
 # Offense count: 72
 # Configuration parameters: EnforcedStyle, SupportedStyles.
 # SupportedStyles: implicit, each, example

spec/bin/changelog_spec.rb

@@ -46,9 +46,7 @@ describe 'bin/changelog' do
     it 'parses -h' do
       expect do
-        $stdout = StringIO.new
-
-        described_class.parse(%w[foo -h bar])
+        expect { described_class.parse(%w[foo -h bar]) }.to output.to_stdout
       end.to raise_error(SystemExit)
     end

spec/tasks/gitlab/gitaly_rake_spec.rb

@@ -84,24 +84,24 @@ describe 'gitlab:gitaly namespace rake task' do
       }
       allow(Gitlab.config.repositories).to receive(:storages).and_return(config)
-      orig_stdout = $stdout
-      $stdout = StringIO.new
-
-      header = ''
+      expected_output = ''
       Timecop.freeze do
-        header = <<~TOML
+        expected_output = <<~TOML
           # Gitaly storage configuration generated from #{Gitlab.config.source} on #{Time.current.to_s(:long)}
           # This is in TOML format suitable for use in Gitaly's config.toml file.
+          [[storage]]
+          name = "default"
+          path = "/path/to/default"
+          [[storage]]
+          name = "nfs_01"
+          path = "/path/to/nfs_01"
         TOML
-        run_rake_task('gitlab:gitaly:storage_config')
       end
-      output = $stdout.string
-      $stdout = orig_stdout
-
-      expect(output).to include(header)
-      parsed_output = TOML.parse(output)
+      expect { run_rake_task('gitlab:gitaly:storage_config')}.
+        to output(expected_output).to_stdout
+      parsed_output = TOML.parse(expected_output)
       config.each do |name, params|
         expect(parsed_output['storage']).to include({ 'name' => name, 'path' => params['path'] })
       end