test: add CLI test coverage

Cover version, help, unknown command, parse_serve_options defaults
and overrides, prepare_config template generation and no-op.

test/cli_test.rb

@@ -0,0 +1,63 @@
+# frozen_string_literal: true
+
+require "test_helper"
+require "tmpdir"
+require "volumen/cli"
+
+class CLITest < Minitest::Test
+  def test_version
+    assert_output("#{Volumen::VERSION}\n") do
+      Volumen::CLI.run(["version"])
+    end
+  end
+
+  def test_help
+    output, = capture_io { Volumen::CLI.run(["help"]) }
+    assert_includes output, "volumen #{Volumen::VERSION}"
+    assert_includes output, "Usage:"
+  end
+
+  def test_unknown_command
+    _output, err = capture_io do
+      assert_raises(SystemExit) { Volumen::CLI.run(["bogus"]) }
+    end
+    assert_includes err, "unknown command"
+  end
+
+  def test_parse_serve_defaults
+    cli = Volumen::CLI.new(["serve"])
+    options = cli.__send__(:parse_serve_options)
+    assert_equal Volumen::Config::DEFAULT_PATH, options[:config]
+  end
+
+  def test_parse_serve_overrides
+    cli = Volumen::CLI.new([
+                             "serve", "--config", "/t.toml", "--host", "127.0.0.1", "--port", "9000"
+                           ])
+    options = cli.__send__(:parse_serve_options)
+    assert_equal "/t.toml", options[:config]
+    assert_equal "127.0.0.1", options[:host]
+    assert_equal 9000, options[:port]
+  end
+
+  def test_prepare_config_writes_template
+    Dir.mktmpdir do |dir|
+      path = File.join(dir, "config.toml")
+      cli = Volumen::CLI.new([])
+      _output, err = capture_io { cli.__send__(:prepare_config, path) }
+      assert_includes err, "wrote a default config"
+      assert_path_exists path
+    end
+  end
+
+  def test_prepare_config_noops_when_present
+    Dir.mktmpdir do |dir|
+      path = File.join(dir, "config.toml")
+      File.write(path, "[server]\nport = 1\n")
+      cli = Volumen::CLI.new([])
+      out, err = capture_io { cli.__send__(:prepare_config, path) }
+      assert_empty err
+      assert_empty out
+    end
+  end
+end