Strings recipes for the Dart Cookbook

recipes/test/core/strings/substituting_strings_test.dart

+library substituting_strings_test;
+
+import 'package:unittest/unittest.dart';
+
+void main() {
+  group('substituting strings based on regExp matches', () {
+    test('using replaceAll()', () {
+      expect('resume'.replaceAll(new RegExp(r'e'), '\u00E9'), equals('résumé'));
+    });
+    
+    test('using replaceFirst()', () {
+      expect('0.0001'.replaceFirst(new RegExp(r'0+'), ''), equals('.0001'));
+    });
+
+    test('using replaceAllMapped()', () {
+      var heart = '\u2661';
+      var string = "I like Ike but I $heart Lucy";
+      var regExp = new RegExp(r'[A-Z]\w+');
+      expect(string.replaceAllMapped(
+        regExp, (match) => match.group(0).toUpperCase()), 
+        equals('I like IKE but I ♡ LUCY'));
+    });
+    
+  });
+}