Add new unit test for testig Pattern.split functionality in Java

This test will be used for testing .NET utilities that equalize
behavior between Java and C# for splitting using regular expressions

DEVSIX-2910

Author: Snipx

io/src/test/java/com/itextpdf/io/util/StringUtilTest.java

@@ -0,0 +1,54 @@
+package com.itextpdf.io.util;
+
+import com.itextpdf.test.annotations.type.UnitTest;
+import org.junit.Assert;
+import org.junit.Test;
+import org.junit.experimental.categories.Category;
+
+import java.util.regex.Pattern;
+
+/**
+ * At the moment there is no StringUtil class in Java, but there is one in C# and we are testing
+ */
+@Category(UnitTest.class)
+public class StringUtilTest {
+
+    @Test
+    public void patternSplitTest01() {
+        // Pattern.split in Java works differently compared to Regex.Split in C#
+        // In C#, empty strings are possible at the beginning of the resultant array for non-capturing groups in split regex
+        // Thus, in C# we use a separate utility for splitting to align the implementation with Java
+        // This test verifies that the resultant behavior is the same
+        Pattern pattern = Pattern.compile("(?=[ab])");
+        String source = "a01aa78ab89b";
+        String[] expected = new String[] {"a01", "a", "a78", "a", "b89", "b"};
+        String[] result = pattern.split(source);
+        Assert.assertArrayEquals(expected, result);
+    }
+
+    @Test
+    public void patternSplitTest02() {
+        Pattern pattern = Pattern.compile("(?=[ab])");
+        String source = "";
+        String[] expected = new String[] {""};
+        String[] result = pattern.split(source);
+        Assert.assertArrayEquals(expected, result);
+    }
+
+    @Test
+    public void stringSplitTest01() {
+        String source = "a01aa78ab89b";
+        String[] expected = new String[] {"a01", "a", "a78", "a", "b89", "b"};
+        String[] result = source.split("(?=[ab])");
+        Assert.assertArrayEquals(expected, result);
+    }
+
+    @Test
+    public void stringSplitTest02() {
+        String source = "";
+        String[] expected = new String[] {""};
+        String[] result = source.split("(?=[ab])");
+        Assert.assertArrayEquals(expected, result);
+    }
+
+}