Add tests showing lambda use. (#103)

Author: matanlurey

test/builders/class_test.dart

@@ -174,6 +174,11 @@ void main() {
         constructor([
           lib$core.print.call([literal('Called constructor')]),
         ]),
+        new MethodBuilder(
+          'toString',
+          returns: literal(r'$Animal'),
+          returnType: lib$core.String,
+        ),
       ]),
       equalsSource(r'''
         class Animal {
@@ -186,6 +191,7 @@ void main() {
           void instanceMethod() {
             print('Called instanceMethod');
           }
+          String toString() => '$Animal';
         }
       '''),
     );

test/builders/method_test.dart

@@ -77,6 +77,15 @@ void main() {
     );
   });
 
+  test('should emit a function with a lambda expression', () {
+    expect(
+      new MethodBuilder('talk', returns: literal('Hello World')),
+      equalsSource(r'''
+        talk() => 'Hello World';
+      '''),
+    );
+  });
+
   group('constructors', () {
     test('should emit a simple constructor', () {
       expect(