Add an explicit distinction between a command's description and summary.

test/command_runner_test.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:args/command_runner.dart';
 import 'package:test/test.dart';
 
 import 'utils.dart';
 
 const _DEFAULT_USAGE = """
@@ skipping 36 matching lines @@
 Global options:
 -h, --help    Print this usage information.
 
 Available commands:
   foo    Set a value.
   help   Display help information for test.
 
 Run "test help <command>" for more information about a command."""));
     });
 
-    test("supports newlines in command descriptions", () {
+    test("truncates newlines in command descriptions by default", () {
       runner.addCommand(new MultilineCommand());
 
       expect(runner.usage, equals("""
 A test command runner.
 
 Usage: test <command> [arguments]
 
 Global options:
 -h, --help    Print this usage information.
 
 Available commands:
   help        Display help information for test.
   multiline   Multi
+
+Run "test help <command>" for more information about a command."""));
+    });
+
+    test("supports newlines in command summaries", () {
+      runner.addCommand(new MultilineSummaryCommand());
+
+      expect(runner.usage, equals("""
+A test command runner.
+
+Usage: test <command> [arguments]
+
+Global options:
+-h, --help    Print this usage information.
+
+Available commands:
+  help        Display help information for test.
+  multiline   Multi
               line.
 
 Run "test help <command>" for more information about a command."""));
     });
 
     test("contains custom options", () {
       runner.argParser.addFlag("foo", help: "Do something.");
 
       expect(runner.usage, equals("""
 A test command runner.
@@ skipping 216 matching lines @@
 
       expect(runner.run(["foo", "bar"]), throwsUsageError(
           'Command "foo" does not take any arguments.', """
 Usage: test foo [arguments]
 -h, --help    Print this usage information.
 
 Run "test help" to see global options."""));
     });
   });
 }