Add version CLI option

features/cli/version.feature

@@ -0,0 +1,6 @@
+Feature: version CLI option
+
+  Scenario: prints the current version on standard output
+    When I run uhwm with option --version
+    Then uhwm must terminate successfully
+    And the output must contain exactly the version

features/steps/output_steps.rb

@@ -10,9 +10,15 @@ options:
     -r, --require PATH               require ruby feature
     -l, --layout LAYOUT              specify layout
     -w, --worker WORKER              specify worker
+    -V, --version                    print version
   eoh
 end
 
+Then /^the output must contain exactly the version$/ do
+  #require File.expand_path('../lib/uh/wm/version', __FILE__)
+  assert_exact_output "%s\n" % Uh::WM::VERSION, all_output
+end
+
 Then /^the output must match \/([^\/]+)\/([a-z]*)$/ do |pattern, options|
   uhwm_wait_output Regexp.new(pattern, options)
 end

lib/uh/wm/cli.rb

@@ -82,6 +82,11 @@ module Uh
               'specify worker' do |worker|
             @env.worker = worker.to_sym
           end
+
+          opts.on_tail '-V', '--version', 'print version' do
+            @env.puts VERSION
+            exit
+          end
         end
       end
     end

spec/uh/wm/cli_spec.rb

@@ -185,6 +185,21 @@ module Uh
           end
         end
 
+        context 'with version option' do
+          let(:arguments) { %w[-V] }
+
+          it 'prints the version on standard output' do
+            trap_exit { cli.parse_arguments! }
+            expect(stdout.string).to eq "#{::Uh::WM::VERSION}\n"
+          end
+
+          it 'exits with a return status of 0' do
+            expect { cli.parse_arguments! }.to raise_error(SystemExit) do |e|
+              expect(e.status).to eq 0
+            end
+          end
+        end
+
         context 'with invalid option' do
           let(:arguments) { %w[--unknown-option] }