Custom extensions in JUnit - Test Execution Trace

Test Overview

This test demonstrates how to use a custom JUnit 5 extension to measure and print the execution time of a test method. It verifies that the extension runs and the test passes.

Test Code - JUnit 5

JUnit

import org.junit.jupiter.api.extension.*;
import org.junit.jupiter.api.*;

class TimingExtension implements BeforeTestExecutionCallback, AfterTestExecutionCallback {
    private static final ExtensionContext.Namespace NAMESPACE = ExtensionContext.Namespace.create("timing");

    @Override
    public void beforeTestExecution(ExtensionContext context) throws Exception {
        context.getStore(NAMESPACE).put("startTime", System.currentTimeMillis());
    }

    @Override
    public void afterTestExecution(ExtensionContext context) throws Exception {
        long startTime = context.getStore(NAMESPACE).remove("startTime", Long.class);
        long duration = System.currentTimeMillis() - startTime;
        System.out.println("Test '" + context.getDisplayName() + "' took " + duration + " ms.");
    }
}

@ExtendWith(TimingExtension.class)
public class CustomExtensionTest {

    @Test
    void sampleTest() {
        Assertions.assertTrue(2 + 2 == 4);
    }
}

Execution Trace - 5 Steps

Step	Action	System State	Assertion	Result
1	JUnit test runner starts the test execution	JUnit framework initialized, test class loaded	-	PASS
2	JUnit calls TimingExtension.beforeTestExecution before sampleTest	Stores current time in extension context store	-	PASS
3	JUnit executes sampleTest method	Inside sampleTest, assertion checks if 2+2 equals 4	assertTrue(2 + 2 == 4)	PASS
4	JUnit calls TimingExtension.afterTestExecution after sampleTest	Calculates elapsed time and prints it to console	-	PASS
5	JUnit completes test execution and reports results	Test passed, timing output visible in console	-	PASS

Failure Scenario

Failing Condition: The assertion in sampleTest fails (e.g., 2 + 2 != 4)

Execution Trace Quiz - 3 Questions

What does the TimingExtension do before the test method runs?

A Stores the current time to measure test duration

B Prints the test name to the console

C Asserts that the test will pass

D Skips the test execution

Key Result

Using custom extensions in JUnit allows you to add reusable behavior around tests, such as timing, logging, or resource management, improving test maintainability and clarity.