Test Doubles

• Dummy (Dummy Object)
  • doesn’t have any data inside
  • can be empty object {}
  • just exists
  • that’s the purpose of the Dummy Object
• Fake
  • has simple data
    • contains simplified data of the object that is replaced by this fake object
    • example: using in-memory db or some “light” db (SQLite?) instead of real db on the project (like PostgreSQL, Oracle)
• Stub
• Spy (in testing)
• Mock
  • it contains expectations about what parameters should be when the function will be called
    • if function was called with different parameters than expected parameters then test will be failed
• Fixtures

Implementation

• For writing all this stuff you can use:
  • Functionality of the framework like JestJS
  • Independent library like Sinon.js