diff --git a/core-java-modules/core-java-regex/src/test/java/com/baeldung/regex/RegexUnitTest.java b/core-java-modules/core-java-regex/src/test/java/com/baeldung/regex/RegexUnitTest.java
index b3c3a91a09..77052b79ac 100644
--- a/core-java-modules/core-java-regex/src/test/java/com/baeldung/regex/RegexUnitTest.java
+++ b/core-java-modules/core-java-regex/src/test/java/com/baeldung/regex/RegexUnitTest.java
@@ -26,7 +26,6 @@ public class RegexUnitTest {
         while (matcher.find())
             matches++;
         assertEquals(matches, 2);
-
     }
 
     @Test
@@ -452,7 +451,6 @@ public class RegexUnitTest {
         Matcher matcher = pattern.matcher("dogs are friendly");
         assertTrue(matcher.lookingAt());
         assertFalse(matcher.matches());
-
     }
 
     @Test
@@ -460,7 +458,6 @@ public class RegexUnitTest {
         Pattern pattern = Pattern.compile("dog");
         Matcher matcher = pattern.matcher("dog");
         assertTrue(matcher.matches());
-
     }
 
     @Test
@@ -469,7 +466,6 @@ public class RegexUnitTest {
         Matcher matcher = pattern.matcher("dogs are domestic animals, dogs are friendly");
         String newStr = matcher.replaceFirst("cat");
         assertEquals("cats are domestic animals, dogs are friendly", newStr);
-
     }
 
     @Test
@@ -478,7 +474,6 @@ public class RegexUnitTest {
         Matcher matcher = pattern.matcher("dogs are domestic animals, dogs are friendly");
         String newStr = matcher.replaceAll("cat");
         assertEquals("cats are domestic animals, cats are friendly", newStr);
-
     }
 
     public synchronized static int runTest(String regex, String text) {
diff --git a/core-java-modules/core-java-regex/src/test/java/com/baeldung/regex/phonenumbers/PhoneNumbersRegexUnitTest.java b/core-java-modules/core-java-regex/src/test/java/com/baeldung/regex/phonenumbers/PhoneNumbersRegexUnitTest.java
new file mode 100644
index 0000000000..11bf1618b6
--- /dev/null
+++ b/core-java-modules/core-java-regex/src/test/java/com/baeldung/regex/phonenumbers/PhoneNumbersRegexUnitTest.java
@@ -0,0 +1,129 @@
+package com.baeldung.regex.phonenumbers;
+
+import static org.junit.Assert.*;
+
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+import org.junit.Test;
+
+public class PhoneNumbersRegexUnitTest {
+
+    @Test
+    public void whenMatchesTenDigitsNumber_thenCorrect() {
+        Pattern pattern = Pattern.compile("^\\d{10}$");
+        Matcher matcher = pattern.matcher("2055550125");
+        assertTrue(matcher.matches());
+    }
+    
+    @Test
+    public void whenMOreThanTenDigits_thenNotCorrect() {
+        Pattern pattern = Pattern.compile("^\\d{10}$");
+        Matcher matcher = pattern.matcher("20555501251");
+        assertFalse(matcher.matches());
+    }
+
+    @Test
+    public void whenMatchesTenDigitsNumberWhitespacesDotHyphen_thenCorrect() {
+        Pattern pattern = Pattern.compile("^(\\d{3}[- .]?){2}\\d{4}$");
+        Matcher matcher = pattern.matcher("202 555 0125");
+        assertTrue(matcher.matches());
+    }
+    
+    @Test
+    public void whenIncludesBracket_thenNotCorrect() {
+        Pattern pattern = Pattern.compile("^(\\d{3}[- .]?){2}\\d{4}$");
+        Matcher matcher = pattern.matcher("202]555 0125");
+        assertFalse(matcher.matches());
+    }
+    
+    @Test
+    public void whenNotStartsWithBatchesOfThreeDigits_thenNotCorrect() {
+        Pattern pattern = Pattern.compile("^(\\d{3}[- .]?){2}\\d{4}$");
+        Matcher matcher = pattern.matcher("2021 555 0125");
+        assertFalse(matcher.matches());
+    }
+    
+    @Test
+    public void whenLastPartWithNoFourDigits_thenNotCorrect() {
+        Pattern pattern = Pattern.compile("^(\\d{3}[- .]?){2}\\d{4}$");
+        Matcher matcher = pattern.matcher("202 555 012");
+        assertFalse(matcher.matches());
+    }
+
+    @Test
+    public void whenMatchesTenDigitsNumberParenthesis_thenCorrect() {
+        Pattern pattern = Pattern.compile("^((\\(\\d{3}\\))|\\d{3})[- .]?\\d{3}[- .]?\\d{4}$");
+        Matcher matcher = pattern.matcher("(202) 555-0125");
+        assertTrue(matcher.matches());
+    }
+
+    @Test
+    public void whenJustOpeningParenthesis_thenNotCorrect() {
+        Pattern pattern = Pattern.compile("^((\\(\\d{3}\\))|\\d{3})[- .]?\\d{3}[- .]?\\d{4}$");
+        Matcher matcher = pattern.matcher("(202 555-0125");
+        assertFalse(matcher.matches());
+    }
+
+    @Test
+    public void whenJustClosingParenthesis_thenNotCorrect() {
+        Pattern pattern = Pattern.compile("^((\\(\\d{3}\\))|\\d{3})[- .]?\\d{3}[- .]?\\d{4}$");
+        Matcher matcher = pattern.matcher("202) 555-0125");
+        assertFalse(matcher.matches());
+    }
+
+    @Test
+    public void whenMatchesTenDigitsNumberPrefix_thenCorrect() {
+        Pattern pattern = Pattern.compile("^(\\+\\d{1,3}( )?)?((\\(\\d{3}\\))|\\d{3})[- .]?\\d{3}[- .]?\\d{4}$");
+        Matcher matcher = pattern.matcher("+111 (202) 555-0125");
+        assertTrue(matcher.matches());
+    }
+
+    @Test
+    public void whenIncorrectPrefix_thenNotCorrect() {
+        Pattern pattern = Pattern.compile("^(\\+\\d{1,3}( )?)?((\\(\\d{3}\\))|\\d{3})[- .]?\\d{3}[- .]?\\d{4}$");
+        Matcher matcher = pattern.matcher("-111 (202) 555-0125");
+        assertFalse(matcher.matches());
+    }
+
+    @Test
+    public void whenTooLongPrefix_thenNotCorrect() {
+        Pattern pattern = Pattern.compile("^(\\+\\d{1,3}( )?)?((\\(\\d{3}\\))|\\d{3})[- .]?\\d{3}[- .]?\\d{4}$");
+        Matcher matcher = pattern.matcher("+1111 (202) 555-0125");
+        assertFalse(matcher.matches());
+    }
+
+    @Test
+    public void whenMatchesPhoneNumber_thenCorrect() {
+        String patterns 
+          = "^(\\+\\d{1,3}( )?)?((\\(\\d{3}\\))|\\d{3})[- .]?\\d{3}[- .]?\\d{4}$"
+          + "|^(\\+\\d{1,3}( )?)?(\\d{3}[ ]?){2}\\d{3}$" 
+          + "|^(\\+\\d{1,3}( )?)?(\\d{3}[ ]?)(\\d{2}[ ]?){2}\\d{2}$";
+
+        String[] validPhoneNumbers 
+          = {"2055550125","202 555 0125", "(202) 555-0125", "+111 (202) 555-0125", "636 856 789", "+111 636 856 789", "636 85 67 89", "+111 636 85 67 89"};
+
+        Pattern pattern = Pattern.compile(patterns);
+        for(String phoneNumber : validPhoneNumbers) {
+            Matcher matcher = pattern.matcher(phoneNumber);
+            assertTrue(matcher.matches());
+        }
+    }
+
+    @Test
+    public void whenNotMatchesPhoneNumber_thenNotCorrect() {
+        String patterns 
+          = "^(\\+\\d{1,3}( )?)?((\\(\\d{3}\\))|\\d{3})[- .]?\\d{3}[- .]?\\d{4}$"
+          + "|^(\\+\\d{1,3}( )?)?(\\d{3}[ ]?){2}\\d{3}$" 
+          + "|^(\\+\\d{1,3}( )?)?(\\d{3}[ ]?)(\\d{2}[ ]?){2}\\d{2}$";
+
+        String[] invalidPhoneNumbers 
+          = {"20555501251","202]555 0125", "2021 555 012", "(202 555-0125", "202) 555-0125", "-111 (202) 555-0125", "+1111 (202) 555-0125", "636 85 789", "636 85 67 893"};
+
+        Pattern pattern = Pattern.compile(patterns);
+        for(String phoneNumber : invalidPhoneNumbers) {
+            Matcher matcher = pattern.matcher(phoneNumber);
+            assertFalse(matcher.matches());
+        }
+    }
+}