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* Fix languages * Missed change for version number * Add language field for presentation * Revert change in README for double buffer Co-authored-by: Jackie Nim <=>
147 lines
3.8 KiB
Markdown
147 lines
3.8 KiB
Markdown
---
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layout: pattern
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title: Arrange/Act/Assert
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folder: arrange-act-assert
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permalink: /patterns/arrange-act-assert/
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categories: Idiom
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language: en
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tags:
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- Testing
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---
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## Also known as
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Given/When/Then
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## Intent
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Arrange/Act/Assert (AAA) is a pattern for organizing unit tests.
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It breaks tests down into three clear and distinct steps:
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1. Arrange: Perform the setup and initialization required for the test.
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2. Act: Take action(s) required for the test.
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3. Assert: Verify the outcome(s) of the test.
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## Explanation
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This pattern has several significant benefits. It creates a clear separation between a test's
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setup, operations, and results. This structure makes the code easier to read and understand. If
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you place the steps in order and format your code to separate them, you can scan a test and
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quickly comprehend what it does.
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It also enforces a certain degree of discipline when you write your tests. You have to think
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clearly about the three steps your test will perform. It makes tests more natural to write at
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the same time since you already have an outline.
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Real world example
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> We need to write comprehensive and clear unit test suite for a class.
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In plain words
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> Arrange/Act/Assert is a testing pattern that organizes tests into three clear steps for easy
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> maintenance.
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WikiWikiWeb says
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> Arrange/Act/Assert is a pattern for arranging and formatting code in UnitTest methods.
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**Programmatic Example**
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Let's first introduce our `Cash` class to be unit tested.
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```java
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public class Cash {
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private int amount;
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Cash(int amount) {
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this.amount = amount;
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}
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void plus(int addend) {
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amount += addend;
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}
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boolean minus(int subtrahend) {
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if (amount >= subtrahend) {
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amount -= subtrahend;
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return true;
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} else {
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return false;
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}
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}
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int count() {
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return amount;
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}
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}
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```
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Then we write our unit tests according to Arrange/Act/Assert pattern. Notice the clearly
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separated steps for each unit test.
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```java
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class CashAAATest {
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@Test
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void testPlus() {
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//Arrange
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var cash = new Cash(3);
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//Act
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cash.plus(4);
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//Assert
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assertEquals(7, cash.count());
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}
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@Test
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void testMinus() {
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//Arrange
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var cash = new Cash(8);
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//Act
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var result = cash.minus(5);
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//Assert
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assertTrue(result);
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assertEquals(3, cash.count());
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}
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@Test
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void testInsufficientMinus() {
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//Arrange
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var cash = new Cash(1);
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//Act
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var result = cash.minus(6);
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//Assert
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assertFalse(result);
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assertEquals(1, cash.count());
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}
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@Test
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void testUpdate() {
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//Arrange
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var cash = new Cash(5);
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//Act
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cash.plus(6);
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var result = cash.minus(3);
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//Assert
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assertTrue(result);
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assertEquals(8, cash.count());
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}
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}
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```
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## Applicability
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Use Arrange/Act/Assert pattern when
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* You need to structure your unit tests so that they're easier to read, maintain, and enhance.
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## Credits
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* [Arrange, Act, Assert: What is AAA Testing?](https://blog.ncrunch.net/post/arrange-act-assert-aaa-testing.aspx)
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* [Bill Wake: 3A – Arrange, Act, Assert](https://xp123.com/articles/3a-arrange-act-assert/)
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* [Martin Fowler: GivenWhenThen](https://martinfowler.com/bliki/GivenWhenThen.html)
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* [xUnit Test Patterns: Refactoring Test Code](https://www.amazon.com/gp/product/0131495054/ref=as_li_qf_asin_il_tl?ie=UTF8&tag=javadesignpat-20&creative=9325&linkCode=as2&creativeASIN=0131495054&linkId=99701e8f4af2f7e8dd50d720c9b63dbf)
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* [Unit Testing Principles, Practices, and Patterns](https://www.amazon.com/gp/product/1617296279/ref=as_li_qf_asin_il_tl?ie=UTF8&tag=javadesignpat-20&creative=9325&linkCode=as2&creativeASIN=1617296279&linkId=74c75cf22a63c3e4758ae08aa0a0cc35)
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* [Test Driven Development: By Example](https://www.amazon.com/gp/product/0321146530/ref=as_li_qf_asin_il_tl?ie=UTF8&tag=javadesignpat-20&creative=9325&linkCode=as2&creativeASIN=0321146530&linkId=5c63a93d8c1175b84ca5087472ef0e05)
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