Principles of a good test

• simple and readable
• tests one component (class, function, etc - one unit) at a time
• independent
• repeatable (known fixed input produces the same known fixed output)
• test the results, not the implementation details

Structure

• setup: create needed objects and dependencies
  • external dependencies (database, network requests, etc) should be mocked so that they don't affect the test results
• execute: run the unit of code being tested
• expect: verify that the result matches what is expected

Types of Mocks

• stub: returns the expected value with no other logic, ignores inputs
• mock: tests that it receives the expected inputs
  • ex. a method on the mock is called 5 times, and/or with the correct arguments
  • tied to implementation: if you change the code such that the method only needs to be called 1 time, the test will fail and need to be updated
• fake: a working implementation, but simplified from the production version
  • ex. an in-memory database
  • fakes can have their own suite of tests

See Also