[Java beginner's anguish] Hard-to-test code implemented in Junit

One day I was writing this code

@Inject
private Accessor accessor;

@Dependent
public class DataReader {

   String getData(String key) {

		String value = accessor.getByDate(key, new Date());

		return value;

	}
}	

Let's test! Here is the test I wrote thinking

public class DataReaderTest {
	
	@Mock
	Accessor accessor;
	
	@InjectMocks @Spy
	DataReader dataReader;
	
	@Before
	public void setUp() throws Exception {
		MockitoAnnotations.initMocks(this);
	}

	@Test
	public void test() {
		when(accessor.getByDate(key, new Date())).thenReturn(now);
		assertThat(dataReader.getData("key0"), is("todayData"));
	}
}

However, when I consulted with him that he wouldn't succeed ... he said, "This won't succeed, it's hard to test."

In Test when (accessor.getByDate (key, new Date ())). thenReturn (now); is actually called ʻaccessor.getByDate (key, getNow ())`, the value of the Date type argument changes. I failed because I ended up

Revised

@Inject
private Accessor accessor;

@Dependent
public class DataReader {

   String getData(String key) {

		String value = accessor.getByDate(key, getNow());

		return value;

	}
	
	Date getNow() {
		return new Date();
	}
}

public class DataReaderReaderTest {
	
	@Mock
	Accessor accessor;
	
	@InjectMocks @Spy
	DataReader dataReader;
	
	@Before
	public void setUp() throws Exception {
		MockitoAnnotations.initMocks(this);
	}

	@Test
	public void test() {
		Date now = new Date();

		//This is also good
		//when(deviceOptionReader.getNow()).thenReturn(now);
		doReturn(now).when(deviceOptionReader).getNow();

		when(accessor.getByDate(key, now)).thenReturn(now);
		assertThat(dataReader.getData("key0"), is("todayData"));
	}
}

Commandments

Do not write code that creates a new Date type directly in the method argument