Agile in a Flash 46

Triple A for Tight Tests – The Code

Agile in a Flash by Jeff Langr and Tim Ottinger (card #46)

> Arrange all the things needed to exercise the code

> Act on the code you want to verify

> Assert that the code worked as expected

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Arrange-Act-Assert (AAA), a simple concept devised by Bill Wake of xp123.com, provides subtle power by helping test readers quickly understand the intent and flow of a test. No more “What the heck is this test even testing?”

In a unit test, you first create, or arrange, a context; then execute, or act on, the target code; and finally assert that the System Under Test (SUT) behaved as expected. Thinking in terms of AAA has direct impact on the code’s visual layout.

The simplest (perhaps ideal) test has three lines, one for each A. Here’s an example where we must verify that the SUT applies late fines to a library patron:

@Test

public void applyFine() {

Patron patron = new Patron(); // arrange the context

patron.setBalance(0);

patron.applyFine(10); // act

assertEquals(10, patron.fineBalance()); // assert

}

You don’t need the comments—the blank lines alone are sufficient.

AAA (also known as given-when-then) isn’t an absolute rule. You might not need an Arrange, and it’s OK to combine an Act and an Assertion into a single-line test.

“Reliability is the degree to which an assessment tool produces stable and consistent results” ~ Phelan, C & Wren, J. (http://www.uni.edu/chfasoa/reliabilityandvalidity.htm)

Testing methodologies:

http://www.guru99.com/testing-methodology.html