This PR is related to BAEL-7554 (#15895)

This PR aims to add a test class "FindLargestNumInStringUnitTest.java".

core-java-modules/core-java-string-operations-8/src/test/java/com/baeldung/findlargestnuminstring/FindLargestNumInStringUnitTest.java

@@ -0,0 +1,59 @@
+package com.baeldung.findlargestnuminstring;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class FindLargestNumInStringUnitTest {
+    String inputString = "The numbers are 10, 20, and 5";
+    int expectedLargestNumber = 20;
+
+    @Test
+    public void givenInputString_whenUsingBasicApproach_thenFindingLargestNumber() {
+        String[] numbers = inputString.split("[^0-9]+");
+
+        int largestNumber = Integer.MIN_VALUE;
+        for (String number : numbers) {
+            if (!number.isEmpty()) {
+                int currentNumber = Integer.parseInt(number);
+                if (currentNumber > largestNumber) {
+                    largestNumber = currentNumber;
+                }
+            }
+        }
+        assertEquals(expectedLargestNumber, largestNumber);
+
+    }
+
+    @Test
+    public void givenInputString_whenUsingRegularExpression_thenFindingLargestNumber() {
+        Pattern pattern = Pattern.compile("\\d+");
+        Matcher matcher = pattern.matcher(inputString);
+
+        int largestNumber = Integer.MIN_VALUE;
+        while (matcher.find()) {
+            int currentNumber = Integer.parseInt(matcher.group());
+            if (currentNumber > largestNumber) {
+                largestNumber = currentNumber;
+            }
+        }
+        assertEquals(expectedLargestNumber, largestNumber);
+
+    }
+
+    @Test
+    public void givenInputString_whenUsingStreamAndLambdaExpression_thenFindingLargestNumber() {
+        int largestNumber = Arrays.stream(inputString.split("[^0-9]+"))
+                .filter(s -> !s.isEmpty())
+                .mapToInt(Integer::parseInt)
+                .max()
+                .orElse(Integer.MIN_VALUE);
+
+        assertEquals(expectedLargestNumber, largestNumber);
+
+    }
+}