Implement basic CLI usage help

spec/uh/wm/cli_spec.rb

@@ -0,0 +1,98 @@
+require 'support/exit_helpers'
+
+module Uh
+  module WM
+    RSpec.describe CLI do
+      include ExitHelpers
+
+      let(:stdout)    { StringIO.new }
+      let(:stderr)    { StringIO.new }
+      let(:arguments) { [] }
+      let(:options)   { { stdout: stdout, stderr: stderr } }
+
+      subject(:cli)   { described_class.new arguments, **options }
+
+      describe '.run' do
+        subject(:run) { described_class.run arguments, **options }
+
+        it 'builds a new CLI with given arguments' do
+          expect(described_class)
+            .to receive(:new).with(arguments, options).and_call_original
+          run
+        end
+
+        it 'parses new CLI arguments' do
+          cli = instance_spy CLI
+          allow(described_class).to receive(:new) { cli }
+          expect(cli).to receive :parse_arguments!
+          run
+        end
+
+        it 'runs new CLI' do
+          cli = instance_spy CLI
+          allow(described_class).to receive(:new) { cli }
+          expect(cli).to receive :run
+          run
+        end
+
+        context 'with invalid arguments' do
+          let(:arguments) { %w[--unknown-option] }
+
+          it 'prints the usage' do
+            expect { trap_exit { run } }.to output(/\AUsage: .+/).to_stderr
+          end
+
+          it 'exits with a return status of 64' do
+            stderr_original = $stderr
+            $stderr = stderr
+            expect { run }.to raise_error(SystemExit) do |e|
+              expect(e.status).to eq 64
+            end
+            $stderr = stderr_original
+          end
+        end
+      end
+
+      describe '#run' do
+        let(:display) { instance_spy Display }
+
+        before { allow(Display).to receive(:new) { display } }
+
+        it 'opens a new X display' do
+          expect(display).to receive :open
+          cli.run
+        end
+
+        it 'prints a message on standard output when connected' do
+          cli.run
+          expect(stdout.string).to match /connected/i
+        end
+      end
+
+      describe '#parse_arguments!' do
+        context 'with help option' do
+          let(:arguments) { %w[-h] }
+
+          it 'prints the usage banner on standard output' do
+            trap_exit { cli.parse_arguments! }
+            expect(stdout.string).to match /\AUsage: .+/
+          end
+
+          it 'prints options usage on standard output' do
+            trap_exit { cli.parse_arguments! }
+            expect(stdout.string).to match /\n^options:\n\s+-/
+          end
+        end
+
+        context 'with invalid option' do
+          let(:arguments) { %w[--unknown-option] }
+
+          it 'raises a CLI::ArgumentError' do
+            expect { cli.parse_arguments! }
+              .to raise_error CLI::ArgumentError
+          end
+        end
+      end
+    end
+  end
+end