Detect SystemExit in tests and convert it to an error

Because if we let it fall through, it'll stop the tests early.
Make sure it's handled.

lib/tasks/gitlab/db.rake

@@ -179,7 +179,7 @@ namespace :gitlab do
     task reindex: :environment do
       unless Gitlab::Database::Reindexing.enabled?
         puts "This feature (database_reindexing) is currently disabled.".color(:yellow)
-        next
+        exit
       end
 
       Gitlab::Database::Reindexing.invoke
@@ -193,7 +193,7 @@ namespace :gitlab do
         task database_name => :environment do
           unless Gitlab::Database::Reindexing.enabled?
             puts "This feature (database_reindexing) is currently disabled.".color(:yellow)
-            next
+            exit
           end
 
           Gitlab::Database::Reindexing.invoke(database_name)

spec/support/system_exit_detected.rb

+# frozen_string_literal: true
+
+SystemExitDetected = Class.new(RuntimeError)
+
+RSpec.configure do |config|
+  config.around do |example|
+    example.run
+  rescue SystemExit
+    # In any cases, we cannot raise SystemExit in the tests,
+    # because it'll skip any following tests from running.
+    # Convert it to something that won't skip everything.
+    # See https://gitlab.com/gitlab-org/gitlab/-/issues/350060
+    raise SystemExitDetected, "SystemExit should be rescued in the tests!"
+  end
+end

spec/tasks/gitlab/db_rake_spec.rb

@@ -214,7 +214,7 @@ RSpec.describe 'gitlab:db namespace rake task', :silence_stdout do
         expect(Gitlab::Database::Reindexing).to receive(:enabled?).and_return(false)
         expect(Gitlab::Database::Reindexing).not_to receive(:invoke)
 
-        run_rake_task('gitlab:db:reindex')
+        expect { run_rake_task('gitlab:db:reindex') }.to raise_error(SystemExit)
       end
     end
   end
@@ -233,7 +233,7 @@ RSpec.describe 'gitlab:db namespace rake task', :silence_stdout do
           expect(Gitlab::Database::Reindexing).to receive(:enabled?).and_return(false)
           expect(Gitlab::Database::Reindexing).not_to receive(:invoke).with(database_name)
 
-          run_rake_task("gitlab:db:reindex:#{database_name}")
+          expect { run_rake_task("gitlab:db:reindex:#{database_name}") }.to raise_error(SystemExit)
         end
       end
     end