13.6. Timeouts

Testing with timeouts

In general, we want to have many small tests that execute quickly.

However, in some situations, we will need to invoke methods in our tests whose execution time is not controllable.

`assertTimeout`

assertTimeout allows us to verify performance levels, i.e., if our methods will finish executing within a given time.

It accepts two parameters.

The expected maximum duration
The code that should run within given duration

Here is an example.

import org.junit.jupiter.api.Test;
import java.time.Duration;
import java.time.temporal.ChronoUnit;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertTimeout;

public class TimeoutTest {
  @Test
  void testShouldCompleteIn1Second() {
    assertTimeout(Duration.of(1000, ChronoUnit.MILLIS), () -> Thread.sleep(3000));
  }

  @Test
  void testShouldCompleteIn1SecondAndReturnValue() {
    String message = assertTimeout(Duration.of(1, ChronoUnit.SECONDS), () -> "Hello, World!");
    assertEquals("Hello, World!", message);
  }
}

When do you think this kind of assertion can be helpful in real life?

`assertTimeoutPreemptively`

An additional related method is assertTimeoutPreemptively.

It stops the execution of the test as soon as the timeout value is exceeded.

To see the difference in behavior, first execute testFinishesInTimePreemptively and then testFinishesInTime:

import org.junit.jupiter.api.Test;

import java.time.Duration;
import java.time.temporal.ChronoUnit;

import static org.junit.jupiter.api.Assertions.*;

public class TimeoutTest {

  @Test
  void testFinishesInTimePreemptively() {
    assertTimeoutPreemptively(Duration.of(1000, ChronoUnit.MILLIS), () -> Thread.sleep(10000));
  }

  @Test
  void testFinishesInTime() {
    assertTimeout(Duration.of(1000, ChronoUnit.MILLIS), () -> Thread.sleep(10000));
  }
}