Introduce span with line context

test/span_test.dart

Index: test/span_test.dart
diff --git a/test/span_test.dart b/test/span_test.dart
index c62753b1a59d66b54c5901deb9cd5155559b068e..08154bd67eda3a9ac7af3efd73ec3ff55de7bb4c 100644
--- a/test/span_test.dart
+++ b/test/span_test.dart
@@ -36,6 +36,22 @@ main() {
       });
     });
 
+    group('for new SourceSpanWithContext()', () {
+      test('contextLine must contain text', () {
+        var start = new SourceLocation(2);
+        var end = new SourceLocation(5);
+        expect(() => new SourceSpanWithContext(
+              start, end, "abc", "--axc--"), throwsArgumentError);
+      });
+
+      test('text starts at start.column in contentLine', () {
+        var start = new SourceLocation(3);
+        var end = new SourceLocation(5);
+        expect(() => new SourceSpanWithContext(
+              start, end, "abc", "--abc--"), throwsArgumentError);
+      });
+    });
+
     group('for union()', () {
       test('source URLs must match', () {
         var other = new SourceSpan(
@@ -178,15 +194,33 @@ foo bar
       expect(span.message("oh no", color: true),
           equals("""
 line 1, column 6 of foo.dart: oh no
-${colors.RED}foo bar
-^^^^^^^${colors.NONE}"""));
+${colors.RED}foo bar${colors.NONE}
+${colors.RED}^^^^^^^${colors.NONE}"""));
     });
 
     test("uses the given color if it's passed", () {
       expect(span.message("oh no", color: colors.YELLOW), equals("""
 line 1, column 6 of foo.dart: oh no
-${colors.YELLOW}foo bar
-^^^^^^^${colors.NONE}"""));
+${colors.YELLOW}foo bar${colors.NONE}
+${colors.YELLOW}^^^^^^^${colors.NONE}"""));
+    });
+  });
+
+  group("message() with context", () {
+    var spanWithContext;
+    setUp(() {
+      spanWithContext = new SourceSpanWithContext(
+          new SourceLocation(5, sourceUrl: "foo.dart"),
+          new SourceLocation(12, sourceUrl: "foo.dart"),
+          "foo bar",
+          "-----foo bar-----");
+    });
+
+    test("underlines under the right column", () {
+      expect(spanWithContext.message("oh no", color: colors.YELLOW), equals("""
+line 1, column 6 of foo.dart: oh no
+-----${colors.YELLOW}foo bar${colors.NONE}-----
+     ${colors.YELLOW}^^^^^^^${colors.NONE}"""));
     });
   });