Unit test: Alerting

In software engineering it's common to ensure the code runs fast enough by triggering an alert when an operation takes too long to execute. Here you are given a class called DurationMonitor which depends on an AlertService. When it receives a duration longer than 1 second (1000 milliseconds = 1 second) it triggers an alert on the AlertService.

Verify that the alert indeed triggers for long durations and does not trigger for durations under a second.

This exercise is part of the course

Introduction to Testing in Java

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Exercise instructions

Verify the alertService mock is called for long durations.
Verify which method on alertService is called for the example long duration, and with what arguments.
Verify in the second test that alertService does not get called.

Hands-on interactive exercise

Have a go at this exercise by completing this sample code.

import org.junit.jupiter.api.Test;
import static com.datacamp.util.testing.CustomJUnitTestLauncher.launchMockitoTestsAndPrint;
import static org.mockito.Mockito.*;

public class Main {
    public static void main(String[] args) {
        launchMockitoTestsAndPrint(DurationMonitorTest.class);
    }
}

class DurationMonitor {
    private AlertService alertService;

    public DurationMonitor(AlertService alertService) {
        this.alertService = alertService;
    }

    public void recordDuration(long durationMillis) {
        if (durationMillis > 1000) {
            alertService.trigger("Slow execution detected: " + durationMillis + "ms");
        } else {
            System.out.println("Execution completed in " + durationMillis + "ms");
        }
    }
}

class DurationMonitorTest {

    @Test
    void recordDuration_triggersAlert_whenAboveLimit() {
        AlertService alertService = mock(AlertService.class);
        DurationMonitor monitor = new DurationMonitor(alertService);
        monitor.recordDuration(1500);

        // Verify alertService.trigger() was called with the expected message
        ____.____("Slow execution detected: 1500ms");
    }

    @Test
    void recordDuration_doesNotTriggerAlert_whenUnderLimit() {
        AlertService alertService = mock(AlertService.class);
        DurationMonitor monitor = new DurationMonitor(alertService);
        monitor.recordDuration(500);

        // Verify alertService was not used
        ____;
    }
}

interface AlertService { void trigger(String message); }

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