diff --git a/src/ArgvParser.php b/src/ArgvParser.php
index f6c2837..a105718 100644
--- a/src/ArgvParser.php
+++ b/src/ArgvParser.php
@@ -36,7 +36,7 @@ class ArgvParser extends Parser
      * @param string $desc
      * @param bool   $allowUnknown
      */
-    public function __construct(string $name, string $desc = null, bool $allowUnknown = false)
+    public function __construct(string $name, string $desc = '', bool $allowUnknown = false)
     {
         $this->_name         = $name;
         $this->_desc         = $desc;
@@ -44,6 +44,10 @@ public function __construct(string $name, string $desc = null, bool $allowUnknow
 
         $this->option('-h, --help', 'Show help')->on([$this, 'showHelp']);
         $this->option('-V, --version', 'Show version')->on([$this, 'showVersion']);
+
+        $this->onExit(function () {
+            exit(0);
+        });
     }
 
     /**
@@ -60,6 +64,16 @@ public function version(string $version): self
         return $this;
     }
 
+    public function getName(): string
+    {
+        return $this->_name;
+    }
+
+    public function getDesc(): string
+    {
+        return $this->_desc;
+    }
+
     /**
      * Registers argument definitions (all at once). Only last one can be variadic.
      *
@@ -137,6 +151,20 @@ public function on(callable $fn): self
         return $this;
     }
 
+    /**
+     * Register exit handler.
+     *
+     * @param callable $fn
+     *
+     * @return self
+     */
+    public function onExit(callable $fn): self
+    {
+        $this->_events['_exit'] = $fn;
+
+        return $this;
+    }
+
     protected function handleUnknown(string $arg, string $value = null)
     {
         if ($this->_allowUnknown) {
@@ -197,22 +225,61 @@ public function args(): array
 
     protected function showHelp()
     {
-        echo "{$this->_name}, version {$this->_version}" . PHP_EOL;
+        $args = $this->_arguments ? ' [ARGUMENTS]' : '';
+        $opts = $this->_options ? ' [OPTIONS]' : '';
+
+        ($w = new Writer)
+            ->bold("Command {$this->_name}, version {$this->_version}", true)->eol()
+            ->comment($this->_desc, true)->eol()
+            ->bold('Usage: ')->yellow("{$this->_name}{$args}{$opts}", true);
+
+        if ($args) {
+            $this->showArguments($w);
+        }
+
+        if ($opts) {
+            $this->showOptions($w);
+        }
+
+        $w->eol()->yellow('Note: <required> [optional]')->eol();
+
+        return $this->emit('_exit');
+    }
+
+    protected function showArguments(Writer $w)
+    {
+        $w->eol()->boldGreen('Arguments:', true);
+
+        $maxLen  = \max(\array_map('strlen', \array_keys($this->_arguments)));
+
+        foreach ($this->_arguments as $arg) {
+            $name = $arg->name();
+            $name = $arg->required() ? "<$name>" : "[$name]";
+            $w->bold('  ' . \str_pad($name, $maxLen + 4))->comment($arg->desc(), true);
+        }
+    }
+
+    protected function showOptions(Writer $w)
+    {
+        $w->eol()->boldGreen('Options:', true);
 
-        // @todo: build help msg!
-        echo "help\n";
+        $maxLen = \max(\array_map('strlen', \array_keys($this->_options)));
 
-        _exit();
+        foreach ($this->_options as $opt) {
+            $name = $opt->short() . '|' . $opt->long();
+            $name = $opt->required() ? "<$name>" : "[$name]";
+            $w->bold('  ' . \str_pad($name, $maxLen + 9))->comment($opt->desc(), true);
+        }
     }
 
     protected function showVersion()
     {
-        echo $this->_version . PHP_EOL;
+        (new Writer)->bold($this->_version, true);
 
-        _exit();
+        return $this->emit('_exit');
     }
 
-    protected function emit(string $event)
+    public function emit(string $event)
     {
         if (empty($this->_events[$event])) {
             return;
@@ -220,15 +287,6 @@ protected function emit(string $event)
 
         $callback = $this->_events[$event];
 
-        $callback();
-    }
-}
-
-// @codeCoverageIgnoreStart
-if (!\function_exists(__NAMESPACE__ . '\\_exit')) {
-    function _exit($code = 0)
-    {
-        exit($code);
+        return $callback();
     }
 }
-// @codeCoverageIgnoreEnd
diff --git a/src/Option.php b/src/Option.php
index e6a9877..6a293a3 100644
--- a/src/Option.php
+++ b/src/Option.php
@@ -18,7 +18,7 @@ class Option extends Parameter
 
     protected $filter;
 
-    public function __construct(string $raw, string $desc = null, $default = null, callable $filter = null)
+    public function __construct(string $raw, string $desc = '', $default = null, callable $filter = null)
     {
         $this->filter = $filter;
 
diff --git a/src/Parameter.php b/src/Parameter.php
index e57406f..2e91d64 100644
--- a/src/Parameter.php
+++ b/src/Parameter.php
@@ -28,7 +28,7 @@ abstract class Parameter
 
     protected $variadic = false;
 
-    public function __construct(string $raw, string $desc = null, $default = null)
+    public function __construct(string $raw, string $desc = '', $default = null)
     {
         $this->raw      = $raw;
         $this->desc     = $desc;
@@ -52,6 +52,11 @@ public function name(): string
         return $this->name;
     }
 
+    public function desc(): string
+    {
+        return $this->desc;
+    }
+
     public function attributeName(): string
     {
         return $this->toCamelCase($this->name);
diff --git a/src/Writer.php b/src/Writer.php
index d1ceebc..c43e9b3 100644
--- a/src/Writer.php
+++ b/src/Writer.php
@@ -45,14 +45,35 @@ public function __get(string $name): self
      * @param string $text
      * @param bool   $eol
      *
-     * @return void
+     * @return self
      */
-    public function write(string $text, bool $eol = false)
+    public function write(string $text, bool $eol = false): self
     {
         list($method, $this->method) = [$this->method ?: 'line', ''];
 
         $stream = \stripos($method, 'error') !== false ? \STDERR : \STDOUT;
 
-        \fwrite($stream, $this->colorizer->{$method}($text, [], $eol));
+        if ($method === 'eol') {
+            \fwrite($stream, PHP_EOL);
+        } else {
+            \fwrite($stream, $this->colorizer->{$method}($text, [], $eol));
+        }
+
+        return $this;
+    }
+
+    /**
+     * Write to stdout or stderr magically.
+     *
+     * @param string $method
+     * @param array  $arguments
+     *
+     * @return self
+     */
+    public function __call(string $method, array $arguments): self
+    {
+        $this->method = $method;
+
+        return $this->write($arguments[0] ?? '', $arguments[1] ?? false);
     }
 }
diff --git a/tests/ArgvParserTest.php b/tests/ArgvParserTest.php
index 2346cad..978088e 100644
--- a/tests/ArgvParserTest.php
+++ b/tests/ArgvParserTest.php
@@ -97,10 +97,6 @@ public function test_options_unknown()
         $p = $this->newParser('', '', true)->parse(['php', '--hot-path', '/path']);
         $this->assertSame('/path', $p->hotPath, 'Allow unknown');
 
-        ob_start();
-        $p = $this->newParser()->parse(['php', '--unknown', '1']);
-        $this->assertContains('help', ob_get_clean(), 'Show help');
-
         $this->expectException(\RuntimeException::class);
         $this->expectExceptionMessage('Option "--random" not registered');
 
@@ -180,22 +176,6 @@ public function test_event()
         $this->assertSame('hello event', ob_get_clean());
     }
 
-    public function test_default_options()
-    {
-        ob_start();
-        $p = $this->newParser('v1.0.1')->parse(['php', '--version']);
-        $this->assertContains('v1.0.1', ob_get_clean(), 'Long');
-
-        ob_start();
-        $p = $this->newParser('v2.0.1')->parse(['php', '-V']);
-        $this->assertContains('v2.0.1', ob_get_clean(), 'Short');
-
-        ob_start();
-        $p = $this->newParser()->parse(['php', '--help']);
-        $this->assertContains('ArgvParserTest', $buffer = ob_get_clean());
-        $this->assertContains('help', $buffer);
-    }
-
     public function test_no_value()
     {
         $p = $this->newParser()->option('-x --xyz')->parse(['php', '-x']);
@@ -211,7 +191,7 @@ public function test_args()
         $this->assertSame(['a' => 'A', 'b' => 'B', 'C', 'D'], $p->args());
     }
 
-    protected function newParser(string $version = '0.0.1', string $desc = null, bool $allowUnknown = false)
+    protected function newParser(string $version = '0.0.1', string $desc = '', bool $allowUnknown = false)
     {
         $p = new ArgvParser('ArgvParserTest', $desc, $allowUnknown);
 
diff --git a/tests/CliTestCase.php b/tests/CliTestCase.php
new file mode 100644
index 0000000..68b06e4
--- /dev/null
+++ b/tests/CliTestCase.php
@@ -0,0 +1,49 @@
+<?php
+
+namespace Ahc\Cli\Test;
+
+use PHPUnit\Framework\TestCase;
+
+/**
+ * To test console output.
+ */
+class CliTestCase extends TestCase
+{
+    public static function setUpBeforeClass()
+    {
+        // Thanks: https://stackoverflow.com/a/39785995
+        stream_filter_register('intercept', StreamInterceptor::class);
+        stream_filter_append(\STDOUT, 'intercept');
+        stream_filter_append(\STDERR, 'intercept');
+    }
+
+    public function setUp()
+    {
+        ob_start();
+        StreamInterceptor::$buffer = '';
+    }
+
+    public function tearDown()
+    {
+        ob_end_clean();
+    }
+
+    public function buffer()
+    {
+        return StreamInterceptor::$buffer;
+    }
+}
+
+class StreamInterceptor extends \php_user_filter
+{
+    public static $buffer = '';
+
+    public function filter($in, $out, &$consumed, $closing)
+    {
+        while ($bucket = stream_bucket_make_writeable($in)) {
+            static::$buffer .= $bucket->data;
+        }
+
+        return PSFS_PASS_ON;
+    }
+}
diff --git a/tests/DefaultOptionTest.php b/tests/DefaultOptionTest.php
new file mode 100644
index 0000000..663fdea
--- /dev/null
+++ b/tests/DefaultOptionTest.php
@@ -0,0 +1,47 @@
+<?php
+
+namespace Ahc\Cli\Test;
+
+use Ahc\Cli\ArgvParser;
+
+class DefaultOptionTest extends CliTestCase
+{
+    public function test_version()
+    {
+        $p = $this->newParser('v1.0.1')->parse(['php', '--version']);
+        $this->assertContains('v1.0.1', $this->buffer(), 'Long');
+    }
+
+    public function test_V()
+    {
+        $p = $this->newParser('v2.0.1')->parse(['php', '-V']);
+        $this->assertContains('v2.0.1', $this->buffer(), 'Short');
+    }
+
+    public function test_help()
+    {
+        $p = $this->newParser()
+            ->arguments('[arg]')
+            ->option('-o --option')
+            ->parse(['php', '--help']);
+
+        $this->assertContains('ArgvParserTest', $buffer = $this->buffer());
+        $this->assertContains('[arg]', $buffer);
+        $this->assertContains('[-o|--option]', $buffer);
+    }
+
+    public function test_help_unknown()
+    {
+        $p = $this->newParser()->arguments('[apple]')->parse(['php', '--unknown', '1']);
+        $this->assertContains('[apple]', $this->buffer(), 'Show help');
+    }
+
+    protected function newParser(string $version = '0.0.1', string $desc = '', bool $allowUnknown = false)
+    {
+        $p = new ArgvParser('ArgvParserTest', $desc, $allowUnknown);
+
+        return $p->version($version)->onExit(function () {
+            return false;
+        });
+    }
+}
diff --git a/tests/WriterTest.php b/tests/WriterTest.php
index 9116b10..dff8594 100644
--- a/tests/WriterTest.php
+++ b/tests/WriterTest.php
@@ -3,66 +3,38 @@
 namespace Ahc\Cli\Test;
 
 use Ahc\Cli\Writer;
-use PHPUnit\Framework\TestCase;
 
-class WriterTest extends TestCase
+class WriterTest extends CliTestCase
 {
-    public static function setUpBeforeClass()
-    {
-        // Thanks: https://stackoverflow.com/a/39785995
-        stream_filter_register('intercept', StreamInterceptor::class);
-        stream_filter_append(\STDOUT, 'intercept');
-        stream_filter_append(\STDERR, 'intercept');
-    }
-
-    public function setUp()
-    {
-        StreamInterceptor::$buffer = '';
-    }
-
     public function test_simple_write()
     {
         (new Writer)->write('Hey');
 
-        $this->assertContains('Hey', StreamInterceptor::$buffer);
-        $this->assertSame("\033[0;37mHey\033[0m", StreamInterceptor::$buffer);
+        $this->assertContains('Hey', $this->buffer());
+        $this->assertSame("\033[0;37mHey\033[0m", $this->buffer());
     }
 
     public function test_write_error()
     {
         (new Writer)->error->write('Something wrong');
 
-        $this->assertContains('Something wrong', StreamInterceptor::$buffer);
-        $this->assertSame("\033[0;31mSomething wrong\033[0m", StreamInterceptor::$buffer);
+        $this->assertContains('Something wrong', $this->buffer());
+        $this->assertSame("\033[0;31mSomething wrong\033[0m", $this->buffer());
     }
 
     public function test_write_with_newline()
     {
         (new Writer)->write('Hello', true);
 
-        $this->assertContains('Hello', StreamInterceptor::$buffer);
-        $this->assertSame("\033[0;37mHello\033[0m" . PHP_EOL, StreamInterceptor::$buffer);
+        $this->assertContains('Hello', $this->buffer());
+        $this->assertSame("\033[0;37mHello\033[0m" . PHP_EOL, $this->buffer());
     }
 
     public function test_write_bold_red_bggreen()
     {
         (new Writer)->bold->red->bgGreen->write('bold->red->bgGreen');
 
-        $this->assertContains('bold->red->bgGreen', StreamInterceptor::$buffer);
-        $this->assertSame("\033[1;31;42mbold->red->bgGreen\033[0m", StreamInterceptor::$buffer);
-    }
-}
-
-class StreamInterceptor extends \php_user_filter
-{
-    public static $buffer = '';
-
-    public function filter($in, $out, &$consumed, $closing)
-    {
-        while ($bucket = stream_bucket_make_writeable($in)) {
-            static::$buffer .= $bucket->data;
-        }
-
-        return PSFS_PASS_ON;
+        $this->assertContains('bold->red->bgGreen', $this->buffer());
+        $this->assertSame("\033[1;31;42mbold->red->bgGreen\033[0m", $this->buffer());
     }
 }
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
index 385ce9c..6c8c4f5 100644
--- a/tests/bootstrap.php
+++ b/tests/bootstrap.php
@@ -1,10 +1,3 @@
 <?php
 
-namespace Ahc\Cli;
-
-function _exit($code = 0)
-{
-    echo "exit($code)";
-}
-
 require_once __DIR__ . '/../vendor/autoload.php';