assertTimeout for performance in JUnit - Build an Automation Script

Verify method completes within 2 seconds using assertTimeout

Preconditions (2)

Step 1: Call the method named 'performHeavyCalculation' without parameters

Step 2: Measure the execution time of the method

Step 3: Verify that the method finishes execution within 2 seconds

✅ Expected Result: The test passes if 'performHeavyCalculation' completes within 2 seconds, otherwise it fails

Automation Requirements - JUnit 5

Assertions Needed:

Use assertTimeout to check method execution time is less than or equal to 2 seconds

Best Practices:

Use lambda expression inside assertTimeout to call the method

Avoid Thread.sleep or manual timing for performance assertion

Keep test method simple and focused on timing assertion

Automated Solution

JUnit

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

public class PerformanceTest {

    // Example method to test
    public void performHeavyCalculation() {
        // Simulate some work
        for (int i = 0; i < 1_000_000; i++) {
            Math.sqrt(i);
        }
    }

    @Test
    public void testPerformHeavyCalculationCompletesWithinTwoSeconds() {
        assertTimeout(Duration.ofSeconds(2), () -> {
            performHeavyCalculation();
        });
    }
}

This test uses JUnit 5's assertTimeout method to check that performHeavyCalculation finishes within 2 seconds.

The Duration.ofSeconds(2) sets the maximum allowed time.

The method call is wrapped in a lambda expression, which assertTimeout runs and measures.

If the method takes longer than 2 seconds, the test fails automatically.

This approach is simple, readable, and uses JUnit's built-in timing features without manual timers.

Common Mistakes - 3 Pitfalls

Using Thread.sleep to simulate timing instead of assertTimeout

Calling the method outside the lambda passed to assertTimeout

Using assertTimeoutPreemptively without understanding it cancels the method on timeout

Bonus Challenge

Now add data-driven testing with 3 different methods that should complete within 2 seconds each

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