Add support for separators.

test/usage_test.dart

 // Copyright (c) 2012, 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.
 
 library usage_test;
 
 import 'package:unittest/unittest.dart';
 import 'package:args/args.dart';
 
 void main() {
@@ skipping 187 matching lines @@
       var parser = new ArgParser();
       parser.addFlag('first', help: 'The first flag');
       parser.addFlag('second-very-long-option', hide: true);
       parser.addFlag('third', help: 'The third flag');
 
       validateUsage(parser, '''
           --[no-]first    The first flag
           --[no-]third    The third flag
           ''');
     });
+
+    group("separators", () {
+      test("separates options where it's placed", () {
+        var parser = new ArgParser();
+        parser.addFlag('zebra', help: 'First');
+        parser.addSeparator('Primate:');
+        parser.addFlag('monkey', help: 'Second');
+        parser.addSeparator('Marsupial:');
+        parser.addFlag('wombat', help: 'Third');
+
+        validateUsage(parser, '''
+            --[no-]zebra     First
+
+            Primate:
+            --[no-]monkey    Second
+
+            Marsupial:
+            --[no-]wombat    Third
+            ''');
+      });
+
+      test("doesn't add extra newlines after a multiline option", () {
+        var parser = new ArgParser();
+        parser.addFlag('zebra', help: 'Multi\nline');
+        parser.addSeparator('Primate:');
+        parser.addFlag('monkey', help: 'Second');
+
+        validateUsage(parser, '''
+            --[no-]zebra     Multi
+                             line
+
+            Primate:
+            --[no-]monkey    Second
+            ''');
+      });
+
+      test("doesn't add newlines if it's the first component", () {
+        var parser = new ArgParser();
+        parser.addSeparator('Equine:');
+        parser.addFlag('zebra', help: 'First');
+
+        validateUsage(parser, '''
+            Equine:
+            --[no-]zebra    First
+            ''');
+      });
+
+      test("doesn't add trailing newlines if it's the last component", () {
+        var parser = new ArgParser();
+        parser.addFlag('zebra', help: 'First');
+        parser.addSeparator('Primate:');
+
+        validateUsage(parser, '''
+            --[no-]zebra    First
+
+            Primate:
+            ''');
+      });
+
+      test("adds a newline after another separator", () {
+        var parser = new ArgParser();
+        parser.addSeparator('First');
+        parser.addSeparator('Second');
+
+        validateUsage(parser, '''
+            First
+
+            Second
+            ''');
+      });
+    });
   });
 }
 
 void validateUsage(ArgParser parser, String expected) {
   expected = unindentString(expected);
   expect(parser.usage, equals(expected));
 }
 
 // TODO(rnystrom): Replace one in test_utils.
 String unindentString(String text) {
@@ skipping 22 matching lines @@
         throw new ArgumentError(
             'Line "$line" does not have enough indentation.');
       }
 
       lines[i] = line.substring(indent);
     }
   }
 
   return lines.join('\n');
 }