This commit is related to the article BAEL-7232 (#15252)

This commit adds a new test class "TimeToLocalDateTimeUnitTest" that shows how to convert a long timestamp into a LocalDateTime object.

core-java-modules/core-java-datetime-conversion/src/test/java/com/baeldung/timestamptolocaldatetime/TimeToLocalDateTimeUnitTest.java

@@ -0,0 +1,42 @@
+package com.baeldung.timestamptolocaldatetime;
+
+import org.joda.time.DateTimeZone;
+import org.junit.Test;
+
+import java.time.Instant;
+import java.time.LocalDateTime;
+import java.time.ZoneId;
+import java.time.format.DateTimeFormatter;
+
+import org.joda.time.DateTime;
+import org.joda.time.format.DateTimeFormat;
+
+import static org.junit.Assert.assertEquals;
+
+public class TimeToLocalDateTimeUnitTest {
+    private static final long timestampInMillis = 1700010123000L;
+    private static final String expectedTimestampString = "2023-11-15 01:02:03";
+
+    @Test
+    public void givenTimestamp_whenConvertingToLocalDateTime_thenConvertSuccessfully() {
+        Instant instant = Instant.ofEpochMilli(timestampInMillis);
+        LocalDateTime localDateTime =
+                LocalDateTime.ofInstant(instant, ZoneId.of("UTC"));
+
+        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
+        String formattedDateTime = localDateTime.format(formatter);
+
+        assertEquals(expectedTimestampString, formattedDateTime);
+    }
+
+    @Test
+    public void givenJodaTime_whenGettingTimestamp_thenConvertToLong() {
+        DateTime dateTime = new DateTime(timestampInMillis, DateTimeZone.UTC);
+        org.joda.time.LocalDateTime localDateTime = dateTime.toLocalDateTime();
+
+        org.joda.time.format.DateTimeFormatter formatter = DateTimeFormat.forPattern("yyyy-MM-dd HH:mm:ss");
+        String actualTimestamp = formatter.print(localDateTime);
+
+        assertEquals(expectedTimestampString, actualTimestamp);
+    }
+}