Clean Tests

Clean Code, Episode 20

Timing:

• 00:00-05:50 introduction
• 05:50-08:30 overview
• 08:30-20:50 astronomy lesson: history of the earth (may skip)
• 20:50-29:50 anatomy of a test
• 29:50-40:57 the arrange
• 40:57-52:55 setup struggles (may skip)
• 52:55-1:06:05 test hierarchy (may skip)
• 1:06:05-1:10:30 clean composition
• 1:10:30-1:20:55 the assertion
• 1:20:55-1:23:10 summary
• 1:23:10-1:24:10 end and credits (may skip)

Vocabulary:

• degenerate test
• setup function - used when there is a group of test functions that share a common arrangement
• teardown function - used when there is a group of test functions that share a common teardown
• fixture - system state needed to run a test
• transient fixture - fixture created and destroyed for a single test
• persistent fixture - fixture that survives from test to test (i.e., shared)
• fresh fixture - fixture that is initialized every time it is used
• shared fixture - fixture that allows some state to accumulate from test to test
• test hierarchy
• composed action
• composed assert

Concepts:

• Four phases of every test function (The Four A’s):

  1. arrange (setup) - set the system into the state necessary to run the test (a.k.a., test fixture)
  2. act (execute)
  3. assert (check)
  4. annihilate (teardown) - undo everything done in the arrange

  Also: given, when, then

• Types of fixtures:

  1. transient fresh - fixture that will be newly created at the beginning of a test method; no teardown is needed (preferred)
     • Means test methods cannot communicate with each other and can be run in any order
  2. persistent fresh - fixture that will be newly created at the beginning of a test method, but that has some persistent state (e.g., open file or other OS resources) that must be managed in the teardown
  3. persistent shared - fixture created and then used by multiple tests (e.g., database connection)

• The Single Assert Rule