Add LineScanner and SpanScanner classes to string_scanner.

pkg/string_scanner/test/error_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.
 
 library string_scanner.error_test;
 
 import 'package:string_scanner/string_scanner.dart';
 import 'package:unittest/unittest.dart';
 
 import 'utils.dart';
 
 void main() {
   test('defaults to the last match', () {
     var scanner = new StringScanner('foo bar baz');
     scanner.expect('foo ');
     scanner.expect('bar');
-    expect(() => scanner.error('oh no!'), throwsFormattedError('''
-Error on line 1, column 5: oh no!
-foo bar baz
-    ^^^'''));
+    expect(() => scanner.error('oh no!'), throwsStringScannerException('bar'));
   });
 
   group("with match", () {
     test('supports an earlier match', () {
       var scanner = new StringScanner('foo bar baz');
       scanner.expect('foo ');
       var match = scanner.lastMatch;
       scanner.expect('bar');
       expect(() => scanner.error('oh no!', match: match),
-          throwsFormattedError('''
-Error on line 1, column 1: oh no!
-foo bar baz
-^^^^'''));
+          throwsStringScannerException('foo '));
     });
 
     test('supports a match on a previous line', () {
       var scanner = new StringScanner('foo bar baz\ndo re mi\nearth fire water');
       scanner.expect('foo bar baz\ndo ');
       scanner.expect('re');
       var match = scanner.lastMatch;
       scanner.expect(' mi\nearth ');
       expect(() => scanner.error('oh no!', match: match),
-          throwsFormattedError('''
-Error on line 2, column 4: oh no!
-do re mi
-   ^^'''));
+          throwsStringScannerException('re'));
     });
 
     test('supports a multiline match', () {
       var scanner = new StringScanner('foo bar baz\ndo re mi\nearth fire water');
       scanner.expect('foo bar ');
       scanner.expect('baz\ndo');
       var match = scanner.lastMatch;
       scanner.expect(' re mi');
       expect(() => scanner.error('oh no!', match: match),
-          throwsFormattedError('''
-Error on line 1, column 9: oh no!
-foo bar baz
-        ^^^'''));
+          throwsStringScannerException('baz\ndo'));
     });
 
     test('supports a match after position', () {
       var scanner = new StringScanner('foo bar baz');
       scanner.expect('foo ');
       scanner.expect('bar');
       var match = scanner.lastMatch;
       scanner.position = 0;
       expect(() => scanner.error('oh no!', match: match),
-          throwsFormattedError('''
-Error on line 1, column 5: oh no!
-foo bar baz
-    ^^^'''));
+          throwsStringScannerException('bar'));
     });
   });
 
   group("with position and/or length", () {
     test('defaults to length 1', () {
       var scanner = new StringScanner('foo bar baz');
       scanner.expect('foo ');
       expect(() => scanner.error('oh no!', position: 1),
-          throwsFormattedError('''
-Error on line 1, column 2: oh no!
-foo bar baz
- ^'''));
+          throwsStringScannerException('o'));
     });
 
     test('defaults to the current position', () {
       var scanner = new StringScanner('foo bar baz');
       scanner.expect('foo ');
       expect(() => scanner.error('oh no!', length: 3),
-          throwsFormattedError('''
-Error on line 1, column 5: oh no!
-foo bar baz
-    ^^^'''));
+          throwsStringScannerException('bar'));
     });
 
     test('supports an earlier position', () {
       var scanner = new StringScanner('foo bar baz');
       scanner.expect('foo ');
       expect(() => scanner.error('oh no!', position: 1, length: 2),
-          throwsFormattedError('''
-Error on line 1, column 2: oh no!
-foo bar baz
- ^^'''));
+          throwsStringScannerException('oo'));
     });
 
     test('supports a position on a previous line', () {
       var scanner = new StringScanner('foo bar baz\ndo re mi\nearth fire water');
       scanner.expect('foo bar baz\ndo re mi\nearth');
       expect(() => scanner.error('oh no!', position: 15, length: 2),
-          throwsFormattedError('''
-Error on line 2, column 4: oh no!
-do re mi
-   ^^'''));
+          throwsStringScannerException('re'));
     });
 
     test('supports a multiline length', () {
       var scanner = new StringScanner('foo bar baz\ndo re mi\nearth fire water');
       scanner.expect('foo bar baz\ndo re mi\nearth');
       expect(() => scanner.error('oh no!', position: 8, length: 8),
-          throwsFormattedError('''
-Error on line 1, column 9: oh no!
-foo bar baz
-        ^^^'''));
+          throwsStringScannerException('baz\ndo r'));
     });
 
     test('supports a position after the current one', () {
       var scanner = new StringScanner('foo bar baz');
       expect(() => scanner.error('oh no!', position: 4, length: 3),
-          throwsFormattedError('''
-Error on line 1, column 5: oh no!
-foo bar baz
-    ^^^'''));
+          throwsStringScannerException('bar'));
+    });
+
+    test('supports a length of zero', () {
+      var scanner = new StringScanner('foo bar baz');
+      expect(() => scanner.error('oh no!', position: 4, length: 0),
+          throwsStringScannerException(''));
     });
   });
 
   group("argument errors", () {
     var scanner;
     setUp(() {
       scanner = new StringScanner('foo bar baz');
       scanner.scan('foo');
     });
 
@@ skipping 10 matching lines @@
     });
 
     test("if position is negative", () {
       expect(() => scanner.error("oh no!", position: -1), throwsArgumentError);
     });
 
     test("if position is outside the string", () {
       expect(() => scanner.error("oh no!", position: 100), throwsArgumentError);
     });
 
-    test("if length is zero", () {
-      expect(() => scanner.error("oh no!", length: 0), throwsArgumentError);
+    test("if position + length is outside the string", () {
+      expect(() => scanner.error("oh no!", position: 7, length: 7),
+          throwsArgumentError);
+    });
+
+    test("if length is negative", () {
+      expect(() => scanner.error("oh no!", length: -1), throwsArgumentError);
     });
   });
 }