Some tests on basic assumptions on Java's LocalDateTime

DateTest.java

import org.junit.Test;

import java.time.Instant;
import java.time.LocalDateTime;
import java.time.Month;
import java.time.ZoneId;

import static org.junit.Assert.assertEquals;

/**
 * @author Jan-Willem Gmelig Meyling
 */
public class DateTest {

	private static ZoneId AMSTERDAM = ZoneId.of("Europe/Amsterdam");

	@Test
	public void verifyEpochIsConvertedToSameDate() throws Exception {
		long now = System.currentTimeMillis();

		Instant instant = Instant.ofEpochMilli(now);
		LocalDateTime res = LocalDateTime.ofInstant(instant, AMSTERDAM);
		assertEquals(now, res.atZone(AMSTERDAM).toInstant().toEpochMilli());
	}

	@Test
	public void verifyEpochIsConvertedToSameDateInSummer() throws Exception {
		LocalDateTime dateInSummer = LocalDateTime.of(2015, 4, 1, 9, 0);
		long now = dateInSummer.atZone(AMSTERDAM).toInstant().toEpochMilli();

		Instant instant = Instant.ofEpochMilli(now);
		LocalDateTime res = LocalDateTime.ofInstant(instant, AMSTERDAM);
		assertEquals(now, res.atZone(AMSTERDAM).toInstant().toEpochMilli());

		// Let's see whether we agree on the date variables
		assertEquals(2015, res.getYear());
		assertEquals(4, res.getMonthValue());
		assertEquals(1, res.getDayOfMonth());
		assertEquals(9, res.getHour());
		assertEquals(0, res.getMinute());

		// Verify that the 4th month is indeed April, and we start counting from 1.
		assertEquals(Month.APRIL, res.getMonth());
	}

	@Test
	public void verifyEpochIsConvertedToSameDateInWinter() throws Exception {
		LocalDateTime dateInSummer = LocalDateTime.of(2015, 10, 26, 9, 0);
		long now = dateInSummer.atZone(AMSTERDAM).toInstant().toEpochMilli();

		Instant instant = Instant.ofEpochMilli(now);
		LocalDateTime res = LocalDateTime.ofInstant(instant, AMSTERDAM);
		assertEquals(now, res.atZone(AMSTERDAM).toInstant().toEpochMilli());

		// Let's see whether we agree on the date variables
		assertEquals(2015, res.getYear());
		assertEquals(10, res.getMonthValue());
		assertEquals(26, res.getDayOfMonth());
		assertEquals(9, res.getHour());
		assertEquals(0, res.getMinute());

		// Verify that the 4th month is indeed October, and we start counting from 1.
		assertEquals(Month.OCTOBER, res.getMonth());
	}

}