Source: Software Testing course at ITMO university by Kochubeev Nikolay Sergeevich 


====== Arrange Act Assert (AAA) ======

Time passes, and [[software_testing|tests]] become unreadable. In just one test there can be way too much arrangement, several actions and dozens of checks. Such a test breaks the main principle: test must explain, not confuse.

Pattern AAA divides test into 3 logical blocks:

  - Arrange -- environment and data preparation.
  - Act -- calling the action being tested.
  - Assert -- result check.

==== Arrange ====
  - Create an object or a system you're checking.
  - Set up dependencies (mock, stub, fake).
  - Prepare the input data.

The test must not make a real connection to the database, it must use a fake or an in-memory storage.

==== Act ====
  - Make one action -- the one you're checking.
  - Do not mix different calls, or else the test will end up checking several things.

==== Assert ====
  - Compare the result to the expected one.
  - Error messages must be informative.
  - It is acceptable to have several asserts, if they test one scenario.

==== Comparing AAA and GWT ====

AAA and [[given_when_then|GWT]] are very similar:
  * Arrange = Given.
  * Act = When.
  * Assert = Then.

AAA is used in testing code, and GWT is used in BDD scenarios, where it's important for them to be readable for the business.

==== AAA violations ====

  - To many actions in Act -- the test checks for several scenarios at once.
  - Long and difficult arrangement -- test is unreadable.
  - No asserts or they're not obvious -- unclear what is being checked.