Implement basic CLI usage help

features/cli/usage.feature

@@ -0,0 +1,11 @@
+Feature: CLI usage
+
+  Scenario: prints the usage when unknown option switch is given
+    When I run uhwm with option --unknown-option
+    Then the exit status must be 64
+    And the output must contain exactly the usage
+
+  Scenario: prints the help when -h option is given
+    When I run uhwm with option -h
+    Then the exit status must be 0
+    And the output must contain exactly the usage

features/steps/output_steps.rb

@@ -0,0 +1,8 @@
+Then /^the output must contain exactly the usage$/ do
+  assert_exact_output <<-eoh, all_output
+Usage: uhwm [options]
+
+options:
+    -h, --help                       print this message
+  eoh
+end

features/steps/run_steps.rb

@@ -1,4 +1,17 @@
-When /^I start uhwm$/ do
-  @process = run 'uhwm'
-  @interactive = @process
+def uhwm_run options = nil
+  command = %w[uhwm]
+  command << options if options
+  @interactive = @process = run command.join ' '
+end
+
+When /^I start uhwm$/ do
+  uhwm_run
+end
+
+When /^I run uhwm with options? (-.+)$/ do |options|
+  uhwm_run options
+end
+
+Then /^the exit status must be (\d+)$/ do |exit_status|
+  assert_exit_status exit_status.to_i
 end