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Testing patterns

Some useful patterns for writing tests or making production code more testable

Humble Object pattern

  • Problem: some behavior is hard to test
    • Example: the way data is presented in the UI
  • Solution:
    • Extract as much of the behavior as possible into an easy-to-test part
    • What's left is a Humble Object containing the hard-to-test stuff stripped down to the bare essence

See also separate note for Humble Object pattern

Clock Wrapper pattern

  • Problem: Behavior depending on current time can be hard to test
  • Solution: Don't get current time directly, but access it through some kind of wrapper that allows you to manually set the time to a specific value for testing purposes
  • Alternative: Pass in current time as a parameter for code you want to keep easy to test (more functional approach)
  • Alternative: Some testing tools can hook into the language's default clock/timers functionality

You can also wrap other dependencies that are hard to control or mock

Object Mother pattern

  • Problem: creating data for tests can be tedious and complex
    • You may need to create a complex hierarchy of objects before you can create object you are interested in
  • Solution: set up an "Object Mother" that creates predefined standard objects with all required data
    • Can make sense to have a few standard objects of the same type to represent variations
      • Example: fresh hire "John" and long-time employee "Heather"
    • Standard objects become familiar to the team and sometimes even enter functional discussions
      • Similar to personas, but not always people: can also be insurance policies, supplier contracts, ...
    • Often, standard objects need a bit of additional setup for the specific test
      • Avoid adding new standard objects, focus on small set that team is familiar with
    • Can have different Object Mothers for different object types
  • Drawback: coupling
    • Many tests will depend on the exact data specified in the Object Mother
    • Changing the standard data can have large impact