Convert shelf to use the string_scanner package.

pkg/string_scanner/test/expect_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_format_test;
+library string_scanner.expect_error_test;
 
 import 'package:string_scanner/string_scanner.dart';
 import 'package:unittest/unittest.dart';
 
+import 'utils.dart';
+
 void main() {
   test('points to the first unconsumed character', () {
     var scanner = new StringScanner('foo bar baz');
     scanner.expect('foo ');
     expect(() => scanner.expect('foo'), throwsFormattedError('''
-Expected "foo" on line 1, column 5.
+Error on line 1, column 5: expected "foo".
 foo bar baz
     ^'''));
   });
 
   test('prints the correct line', () {
     var scanner = new StringScanner('foo bar baz\ndo re mi\nearth fire water');
     scanner.expect('foo bar baz\ndo ');
     expect(() => scanner.expect('foo'), throwsFormattedError('''
-Expected "foo" on line 2, column 4.
+Error on line 2, column 4: expected "foo".
 do re mi
    ^'''));
   });
 
   test('handles the beginning of the string correctly', () {
     var scanner = new StringScanner('foo bar baz');
     expect(() => scanner.expect('zap'), throwsFormattedError('''
-Expected "zap" on line 1, column 1.
+Error on line 1, column 1: expected "zap".
 foo bar baz
 ^'''));
   });
 
   test('handles the end of the string correctly', () {
     var scanner = new StringScanner('foo bar baz');
     scanner.expect('foo bar baz');
     expect(() => scanner.expect('bang'), throwsFormattedError('''
-Expected "bang" on line 1, column 12.
+Error on line 1, column 12: expected "bang".
 foo bar baz
            ^'''));
   });
 
   test('handles an empty string correctly', () {
     expect(() => new StringScanner('').expect('foo'), throwsFormattedError('''
-Expected "foo" on line 1, column 1.
+Error on line 1, column 1: expected "foo".
 
 ^'''));
   });
 
   group("expected name", () {
     test("uses the provided name", () {
       expect(() => new StringScanner('').expect('foo bar', name: 'zap'),
           throwsFormattedError('''
-Expected zap on line 1, column 1.
+Error on line 1, column 1: expected zap.
 
 ^'''));
     });
 
     test("escapes string quotes", () {
       expect(() => new StringScanner('').expect('foo"bar'),
           throwsFormattedError('''
-Expected "foo\\"bar" on line 1, column 1.
+Error on line 1, column 1: expected "foo\\"bar".
 
 ^'''));
     });
 
     test("escapes string backslashes", () {
       expect(() => new StringScanner('').expect('foo\\bar'),
           throwsFormattedError('''
-Expected "foo\\\\bar" on line 1, column 1.
+Error on line 1, column 1: expected "foo\\\\bar".
 
 ^'''));
     });
 
     test("prints PERL-style regexps", () {
       expect(() => new StringScanner('').expect(new RegExp(r'foo')),
           throwsFormattedError('''
-Expected /foo/ on line 1, column 1.
+Error on line 1, column 1: expected /foo/.
 
 ^'''));
     });
 
     test("escape regexp forward slashes", () {
       expect(() => new StringScanner('').expect(new RegExp(r'foo/bar')),
           throwsFormattedError('''
-Expected /foo\\/bar/ on line 1, column 1.
+Error on line 1, column 1: expected /foo\\/bar/.
 
 ^'''));
     });
 
     test("does not escape regexp backslashes", () {
       expect(() => new StringScanner('').expect(new RegExp(r'foo\bar')),
           throwsFormattedError('''
-Expected /foo\\bar/ on line 1, column 1.
+Error on line 1, column 1: expected /foo\\bar/.
 
 ^'''));
     });
   });
 }
-
-Matcher throwsFormattedError(String format) {
-  return throwsA(predicate((error) {
-    expect(error, isFormatException);
-    expect(error.message, equals(format));
-    return true;
-  }));
-}