How to mock UUID.randomUuid() and System.currentTimeMillis() without PowerMock? - junit

Question

I am improving my code coverage, and I am using Sonar to compute it.
But Sonar and PowerMock are not very compatible. I was wondering if there is another way to mock UUID.randomUUID() and System.currentTimeMillis() methods without using PowerMock?

Answer 1

I know that PowerMock can introduce difficulties, but I'm not aware of any reason why SonarQube would be incompatible with it.
In any case, recent versions of Mockito can mock static methods (although I haven't used this yet): https://www.baeldung.com/mockito-mock-static-methods .

Answer 2

As rightly noted by #Augusto, one should introduce dependencies instead of relying on static method calls. Then you won't need powermock at all.
Assuming your tools are JUnit5, assertj and mockito. An example goes like this:
// -- production code --
import java.util.UUID;
import java.util.function.Supplier;
public class ProductionCode {
private final Supplier<String> idSupplier;
private final Supplier<Long> clock;
// #VisibleForTesting
ProductionCode(Supplier<String> idSupplier, Supplier<Long> clock) {
this.idSupplier = idSupplier;
this.clock = clock;
}
public ProductionCode() {
this(() -> UUID.randomUUID().toString(), System::currentTimeMillis);
}
public String methodUnderTest() {
return String.format("%s -- %d", idSupplier.get(), clock.get());
}
}
// -- test code without mocking
import static org.assertj.core.api.Assertions.assertThat;
import org.junit.jupiter.api.Test;
public class Tests {
#Test
void methodUnderTest_shouldSeparateByDoubleDashRandomIdAndCurrentTime() {
ProductionCode objectUnderTest = new ProductionCode(() -> "id", () -> 1234L);
String s = objectUnderTest.methodUnderTest();
assertThat(s).isEqualTo("id -- 1234");
}
}
// -- test code (mockito) --
import static org.assertj.core.api.Assertions.assertThat;
import java.util.function.Supplier;
import org.junit.jupiter.api.Test;
import org.mockito.Mockito;
public class Tests {
private final Supplier<String> idSupplier = Mockito.mock(Supplier.class);
private final Supplier<Long> clock = Mockito.mock(Supplier.class);
private final ProductionCode objectUnderTest = new ProductionCode(idSupplier, clock);
#Test
void methodUnderTest_shouldSeparateRandomIdAndCurrentTimeByDoubleDash() {
Mockito.when(idSupplier.get()).thenReturn("id");
Mockito.when(clock.get()).thenReturn(1234L);
String s = objectUnderTest.methodUnderTest();
assertThat(s).isEqualTo("id -- 1234");
}
}