test-structure-anatomy

Divide the test body into Arrange, Act, and Assert blocks separated by blank lines. Keep Act to a single call, limit Assert to one concern, and include only setup that affects the result. Verify the test fails on the intended line by temporarily breaking the expectation.

They are structurally identical three-stage patterns. Given-When-Then uses business vocabulary (precondition, operation, result) suited to acceptance tests and Gherkin scenarios, while AAA uses technical vocabulary for general unit tests.

Build a cases array of input, expected value, and label rows, then pass it to it.each with dynamic placeholders like $partition and $value in the test name. Keep one shared assertion expression and hardcode expected values rather than computing them.

Split the table when the verification differs per row, such as mixing value checks with exception checks. Branching logic like if statements inside an it.each callback signals the table actually contains multiple behaviors and violates one-test-one-behavior.

Multiple unrelated assertions make one test span several behaviors, breaking the one-to-one mapping between tests and ledger entries. This makes coverage uncountable and failure diagnosis ambiguous, so each test verifies exactly one behavior.