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Test Hooks - Part II

To properly test the use of the timestamp, we follow the dependency inversion principle again here and a test hook to set an instance of the Clock abstract class we use for generating the creation timestamp:

import org.easymock.EasyMock;
import org.testng.annotations.Test;
import java.time.Clock;
import java.time.Instant;
import java.time.ZoneId;
interface DataLayer {
void insertReminder(
final Reminder reminder,
final long creationTimestampInMillis);
class Reminder {
// Reminder fields go here
class Orchestrator {
private final DataLayer dataLayer;
private Clock clock = Clock.systemUTC(); // for testability
public Orchestrator(final DataLayer dataLayer) {
this.dataLayer = dataLayer;
void setClock(final Clock clock) {
this.clock = clock;
public void addReminder(final Reminder reminder) {
// Validation and pre-processing code goes here
dataLayer.insertReminder(reminder, this.clock.millis());
// ...
public class OrchestratorTest {
public void testAddReminder() throws Exception {
final Reminder reminderToAdd = new Reminder();
final DataLayer dataLayerMock =
final Orchestrator orchestrator =
new Orchestrator(dataLayerMock);
final long creationTimestampInMillis =
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