The Arrange–Act–Assert (AAA) pattern gives a unit test three focused stages: prepare the test environment, execute the behavior under test, and verify the expected result. Keeping this structure prevents tests from drifting into unclear or ineffective forms. section 10.2
Use the stages deliberately:
- Arrange: create and configure helper objects or other test data; omit this stage only when setup is unnecessary. section 10.2
- Act: execute the function or behavior being tested once the environment is ready. section 10.2
- Assert: check that the result matches expectations, using the assertion suited to the value being tested. section 10.2
- Keep assertions after the action, especially when computation is parallel; collect asynchronous results in the original test thread before asserting. section 10.5
A passing test that tests nothing
Using assertNotNull(data.isEmpty()) instead of assertTrue(data.isEmpty()) or assertFalse(data.isEmpty()) can make a test always pass. The boolean result is autoboxed to a Boolean object, which is never null, so the assertion ignores the actual truth value. Also verify assertion argument order when optional message parameters are supported. section 10.2
Future<?> f1 = executor.submit(new AsyncRequest("/r1"));
Future<?> f2 = executor.submit(new AsyncRequest("/r2"));
f1.get();
f2.get();
Use Future results to transfer failures from parallel work back to the test thread before performing assertions. section 10.5
