Introduce span with line context

test/file_message_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:unittest/unittest.dart';
 import 'package:source_span/source_span.dart';
 import 'package:source_span/src/colors.dart' as colors;
 
 main() {
   var file;
@@ skipping 42 matching lines @@
   });
 
   test("works for a point span at the end of the file", () {
     expect(file.location(38).pointSpan().message("oh no"), equals("""
 line 3, column 12 of foo.dart: oh no
 zip zap zop
            ^"""));
   });
 
   test("works for a point span in an empty file", () {
-    expect(new SourceFile("").location(0).pointSpan().message("oh no"),
-        equals("""
+    expect(new SourceFile("").location(0).pointSpan().message("oh no"), equals(
+        """
 line 1, column 1: oh no
 
 ^"""));
   });
 
   test("works for a single-line file without a newline", () {
-    expect(new SourceFile("foo bar").span(0, 7).message("oh no"),
-        equals("""
+    expect(new SourceFile("foo bar").span(0, 7).message("oh no"), equals("""
 line 1, column 1: oh no
 foo bar
 ^^^^^^^"""));
   });
 
   group("colors", () {
     test("doesn't colorize if color is false", () {
       expect(file.span(4, 7).message("oh no", color: false), equals("""
 line 1, column 5 of foo.dart: oh no
 foo bar baz
     ^^^"""));
     });
 
     test("colorizes if color is true", () {
       expect(file.span(4, 7).message("oh no", color: true), equals("""
 line 1, column 5 of foo.dart: oh no
 foo ${colors.RED}bar${colors.NONE} baz
     ${colors.RED}^^^${colors.NONE}"""));
     });
 
     test("uses the given color if it's passed", () {
       expect(file.span(4, 7).message("oh no", color: colors.YELLOW), equals("""
 line 1, column 5 of foo.dart: oh no
 foo ${colors.YELLOW}bar${colors.NONE} baz
     ${colors.YELLOW}^^^${colors.NONE}"""));
     });
   });
 }