Strings recipes for the Dart Cookbook

recipes/test/core/strings/interpolating_expressions_test.dart

Index: recipes/test/core/strings/interpolating_expressions_test.dart
diff --git a/recipes/test/core/strings/interpolating_expressions_test.dart b/recipes/test/core/strings/interpolating_expressions_test.dart
new file mode 100644
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+++ b/recipes/test/core/strings/interpolating_expressions_test.dart
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+library interpolating_expressions_test;
+
+import 'package:unittest/unittest.dart';
+
+class Point {
+  num x, y;
+  Point(this.x, this.y);
+}
+
+class PointWithToString {
+  num x, y;
+  PointWithToString(this.x, this.y);
+  
+  String toString() => 'x: $x, y: $y';
+}
+
+void main() {
+  group('interpolating expressions', () {
+    test('without {}', () {
+      var favFood = 'sushi';
+      expect('I love ${favFood.toUpperCase()}', equals('I love SUSHI')); 
+      expect('I love $favFood', equals('I love sushi'));
+    });
+    
+    test('with implicit toString()', () {
+      var four = 4;
+      expect('The $four seasons', equals('The 4 seasons'));
+      expect('The '.concat(4.toString()).concat(' seasons'), equals('The 4 seasons'));
+       
+      var point = new Point(3, 4);
+      expect('Point: $point', equals("Point: Instance of 'Point'"));
+    });
+    
+    test('with explicit toString()', () {
+      var point = new PointWithToString(3, 4);
+      expect('Point: $point', equals('Point: x: 3, y: 4'));
+      
+    });
+  });
+}