Add couple of cases for RegExp test class

src/test/java/by/andd3dfx/regexp/RegExpCheckerTest.java

@@ -16,6 +16,12 @@
  */
 public class RegExpCheckerTest {
 
+    @Test
+    public void ipAddressRegExp() {
+        assertThat(extractStringByRegExp("((\\d{1,2}|1\\d{2}|2[0-5]{2})\\.){3}((\\d{1,2}|1\\d{2}|2[0-5]{2}))",
+                        "Bla, some ip-address 192.168.1.1 here."), is("192.168.1.1"));
+    }
+
     @Test
     public void repeatableExpressions() {
         assertThat("Color should be found",
@@ -56,6 +62,13 @@ public void lookForwardAndBackward() {
             is("30"));
     }
 
+    @Test
+    public void reuseAlreadyDeclaredExpressionWithLinkAndLookForwardAndBackward() {
+        assertThat("Inner content of tag <h1> should be found",
+                extractStringByRegExp("(?<=<([hH][1-6])>).*(?=</\\1>)", "Bla, some <h1>test string</h1> here."),
+                is("test string"));
+    }
+
     @Test
     public void compositeExpression() {
         assertThat("Phone in +ddd-dd-ddd-dd-dd format should be found",