Mockito Unit Test void function in a class - unit-testing

Question

I am fairly new to Mockito. I am not sure how to test the void function emitcount() or to actually test the class to 100%?
#AllArgsConstructor(onConstructor = #__(#Inject))
public class MetricsFactoryProvider {
private MetricsFactory metricsHelper;
public void emitCount(final String metricName, final double metricCount, final long startTime) {
if (StringUtils.isBlank(metricName)) {
return;
}
try {
Metrics metrics = metricsHelper.newMetrics();
metrics.addDate("StartTime", startTime);
metrics.addCount(metricName, metricCount, Unit.ONE);
metrics.close();
} catch (Throwable t) {
throw some exception();
}
}
This is the code I have so far
public class MetricsFactoryProviderTest {
#Mock
Metrics metrics;
#Mock
MetricsFactory metricsHelper;
public void testemitCountfromMetricsFactoryProvider() {
metricsHelper = new MetricsHelper();
Metrics metrics = metricsHelper.newMetrics();
metrics.addDate("StartTime", System.currentTimeMillis());
metrics.addCount("some", 1, Unit.ONE);
MetricsFactoryProvider metricsFactoryProvider = new MetricsFactoryProvider(metrics.getMetricsFactory());
metricsFactoryProvider.emitCount("some metric name",1,System.currentTimeMillis());
Assert.assertNotNull(metricsFactoryProvider);
}
How do I test emitfunction? My thought process
donothing(when(metricsFactoryProvider.emitfunction(pass args)))
Or Do I have to use ArgumentCaptor() ? How do I verify that the function emitfunction is called and metricsFactoryProvider object has correct data?

Answer 1

This here:
#Mock
Metrics metrics;
together with
Metrics metrics = new MetricsHelper().newMetrics();
simply doesn't make any sense. Your test class defines a mocked Metrics object - but then create another real metrics objects which you then pass to your class under test.
It is pretty simple: when you can verify the expected behavior using a real object - then do that. Otherwise, you use a mock.
And then you could do things like
MetricsFactoryProvider underTest = new MetricsFactoryProvider(mockedHelper);
underTest.emit(...);
verify(mockedHelper).add(eq("Start Date"), any());
just for example. In that sense: don't try to learn mocking by trial and error. It is too complicated for that. Instead: read and follow a good tutorial, like this one.
But just to give a short hint here: there are two different cases for using mocks.
Whatever mockedFoo = mock(Whatever.class);
when(mockedFoo.bar()).thenReturn("something else");
UnderTest underTest = new UnderTest(mockedFoo);
assertThat(underTest.foo(), is("something else"));
The above uses a "mocking specification" so that the class under test can do its job. You need to control the mock to do something inside your test. Compare that to:
Whatever mockedFoo = mock(Whatever.class);
UnderTest underTest = new UnderTest(mockedFoo);
assertThat(underTest.foo(), is("something else"));
verify(mockedFoo).bar("expected"parm");
In this case, you want check that a certain expected call happened.