New ConsoleHelper module

.write_stderr
.format_for_stderr

lib/console_helper.rb

+# frozen_string_literal: true
+
+module ConsoleHelper
+  LINE_PREFACE = '> GitLab:'
+
+  def write_stderr(messages)
+    format_for_stderr(messages).each do |message|
+      $stderr.puts(message)
+    end
+  end
+
+  def format_for_stderr(messages)
+    Array(messages).each_with_object([]) do |message, all|
+      all << "#{LINE_PREFACE} #{message}" unless message.empty?
+    end
+  end
+end

spec/console_helper_spec.rb

+require_relative 'spec_helper'
+require_relative '../lib/console_helper'
+
+describe ConsoleHelper do
+  using RSpec::Parameterized::TableSyntax
+
+  class DummyClass
+    include ConsoleHelper
+  end
+
+  subject { DummyClass.new }
+
+  describe '#write_stderr' do
+    where(:messages, :stderr_output) do
+      'test'          | "> GitLab: test\n"
+      %w{test1 test2} | "> GitLab: test1\n> GitLab: test2\n"
+    end
+
+    with_them do
+      it 'puts to $stderr, prefaced with > GitLab:' do
+        expect { subject.write_stderr(messages) }.to output(stderr_output).to_stderr
+      end
+    end
+  end
+
+  describe '#format_for_stderr' do
+    where(:messages, :result) do
+      'test'          | ['> GitLab: test']
+      %w{test1 test2} | ['> GitLab: test1', '> GitLab: test2']
+    end
+
+    with_them do
+      it 'returns message(s), prefaced with > GitLab:' do
+          expect(subject.format_for_stderr(messages)).to eq(result)
+      end
+    end
+  end
+end