BAEL-5465: tests for subtracting days from date (#11954)

* BAEL-5465: tests for subtracting days from date

* BAEL-5465: upated readme

core-java-modules/core-java-date-operations-2/src/test/java/com/baeldung/subtractdays/SubtractDaysFromDateUnitTest.java

@@ -0,0 +1,49 @@
+package com.baeldung.subtractdays;
+
+import static org.junit.Assert.assertEquals;
+
+import java.text.SimpleDateFormat;
+import java.time.LocalDate;
+import java.util.Calendar;
+import java.util.Date;
+import java.util.GregorianCalendar;
+
+import org.joda.time.DateTime;
+import org.junit.Test;
+
+public class SubtractDaysFromDateUnitTest {
+
+    @Test
+    public void givenCalendarDate_whenSubtractingFiveDays_dateIsChangedCorrectly() {
+        Calendar calendar = Calendar.getInstance();
+        calendar.set(2022, Calendar.APRIL, 20);
+
+        calendar.add(Calendar.DATE, -5);
+
+        assertEquals(15, calendar.get(Calendar.DAY_OF_MONTH));
+        assertEquals(Calendar.APRIL, calendar.get(Calendar.MONTH));
+        assertEquals(2022, calendar.get(Calendar.YEAR));
+    }
+
+    @Test
+    public void givenJodaDateTime_whenSubtractingFiveDays_dateIsChangedCorrectly() {
+        DateTime dateTime = new DateTime(2022, 4, 20, 12, 0, 0);
+
+        dateTime = dateTime.minusDays(5);
+
+        assertEquals(15, dateTime.getDayOfMonth());
+        assertEquals(4, dateTime.getMonthOfYear());
+        assertEquals(2022, dateTime.getYear());
+    }
+
+    @Test
+    public void givenLocalDateTime_whenSubtractingFiveDays_dateIsChangedCorrectly() {
+        LocalDate localDateTime = LocalDate.of(2022, 4, 20);
+
+        localDateTime = localDateTime.minusDays(5);
+
+        assertEquals(15, localDateTime.getDayOfMonth());
+        assertEquals(4, localDateTime.getMonthValue());
+        assertEquals(2022, localDateTime.getYear());
+    }
+}