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Java Design Patterns

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

    TestingCode simplificationIsolationTestingAbout 2 min

    On This Page

    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:

    1. Arrange: You set up the venue, prepare the guest list, arrange seating, and organize the catering.
    2. Act: You conduct the event according to the plan, welcoming guests, serving food, and following the schedule.
    3. 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.

    Flowchart

    Arrange/Act/Assert flowchart
    Arrange/Act/Assert flowchart

    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 ourCash 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.

    Related Java Design Patterns

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

    References and Credits


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