2022-06-09-shared-clock

Shared clock

Decision

A mockable shared Clock is used across EDC modules to get the time.

Other mechanisms for accessing the time, such as calls to Instant.now(), new Date(), or System.currentTimeMillis() shall not be used in production code. They may be used in test code.

Rationale

This allows writing consistent test code with assertions about time behavior.

Approach

The shared clock can be injected in service extensions:

@Inject
private Clock clock;

or with a convenience method:

@Override
public void initialize(ServiceExtensionContext context) {
  var clock = context.getClock();
  ...
}

By default, this provides the system clock. In integration tests, another Clock implementation can be registered through mocking:

@ExtendWith(EdcExtension.class)
class AnIntegrationTest {
  @BeforeEach
  void setUp(EdcExtension extension) {
    extension.registerServiceMock(Clock.class, Clock.fixed(now, UTC));
  }
}