Arrange/Act/Assert Pattern in Java: Enhance Testing Clarity and Simplicity

About 2 min

Also known as

Given/When/Then

Intent of Arrange/Act/Assert Design Pattern

The Arrange/Act/Assert pattern is essential in unit testing in Java. This testing method structures unit tests clearly by dividing them into three distinct sections: setup (Arrange), execution (Act), and verification (Assert).

Detailed Explanation of Arrange/Act/Assert Pattern with Real-World Examples

Real-world example

Imagine you are organizing a small event. To ensure everything runs smoothly, you follow a pattern similar to Arrange/Act/Assert:
Arrange: You set up the venue, prepare the guest list, arrange seating, and organize the catering.
Act: You conduct the event according to the plan, welcoming guests, serving food, and following the schedule.
Assert: After the event, you evaluate its success by checking guest feedback, ensuring all tasks were completed, and reviewing if everything went as planned.
This clear separation of preparation, execution, and evaluation helps ensure the event is well-organized and successful, mirroring the structured approach of the Arrange/Act/Assert pattern in software testing.

In plain words

Arrange/Act/Assert is a testing pattern that organizes tests into three clear steps for easy maintenance.

WikiWikiWeb says

Arrange/Act/Assert is a pattern for arranging and formatting code in UnitTest methods.

Programmatic Example of Arrange/Act/Assert Pattern in Java

We need to write comprehensive and clear unit test suite for a class. Using the Arrange/Act/Assert pattern in Java testing ensures clarity.

Let's first introduce our Cash class to be unit tested.

public class Cash {

    private int amount;

    Cash(int amount) {
        this.amount = amount;
    }

    void plus(int addend) {
        amount += addend;
    }

    boolean minus(int subtrahend) {
        if (amount >= subtrahend) {
            amount -= subtrahend;
            return true;
        } else {
            return false;
        }
    }

    int count() {
        return amount;
    }
}

Then we write our unit tests according to Arrange/Act/Assert pattern. Notice the clearly separated steps for each unit test.

class CashAAATest {

    @Test
    void testPlus() {
        //Arrange
        var cash = new Cash(3);
        //Act
        cash.plus(4);
        //Assert
        assertEquals(7, cash.count());
    }

    @Test
    void testMinus() {
        //Arrange
        var cash = new Cash(8);
        //Act
        var result = cash.minus(5);
        //Assert
        assertTrue(result);
        assertEquals(3, cash.count());
    }

    @Test
    void testInsufficientMinus() {
        //Arrange
        var cash = new Cash(1);
        //Act
        var result = cash.minus(6);
        //Assert
        assertFalse(result);
        assertEquals(1, cash.count());
    }

    @Test
    void testUpdate() {
        //Arrange
        var cash = new Cash(5);
        //Act
        cash.plus(6);
        var result = cash.minus(3);
        //Assert
        assertTrue(result);
        assertEquals(8, cash.count());
    }
}

When to Use the Arrange/Act/Assert Pattern in Java

Use Arrange/Act/Assert pattern when

Unit testing, especially within the context of TDD and BDD
Anywhere clarity and structure are needed in test cases

Real-World Applications of Arrange/Act/Assert Pattern in Java

This pattern is particularly useful when practicing TDD and/or BDD methodologies in Java.
Utilized in various programming languages and testing frameworks, such as JUnit (Java), NUnit (.NET), and xUnit frameworks.

Benefits and Trade-offs of Arrange/Act/Assert Pattern

Benefits:

Improved readability of tests by clearly separating the setup, action, and verification steps.
Easier maintenance and understanding of tests, as each test is structured in a predictable way.
Facilitates debugging by isolating test failures to specific phases within the test.

Trade-offs:

May introduce redundancy in tests, as similar arrangements may be repeated across tests.
Some complex tests might not fit neatly into this structure, requiring additional context or setup outside these three phases.

Page Object: A pattern for organizing UI tests that can be used in conjunction with Arrange/Act/Assert.