How do you work with contracts during the development of a new service when contracts are not finalized and often change?

When working with changing contracts during the development of a new service, it is useful to employ the following approaches:

• Versioning of contracts. Create versions of APIs or contracts to support multiple options simultaneously and gradually migrate clients.

• Using mocks and stubs. Until the contract is finalized, work with mock implementations that are easy to update when changes occur.

• Contract testing. Tools like Pact allow verifying the compliance between services even when changes happen.

• Frequent communication with the team. Quick feedback and discussion of changes help avoid misunderstandings.

• Flexible architecture. Design the service so that changes in the contract minimally affect the internal logic.

Example: In Go, interfaces and mock structures can be used, which are easy to change when contracts change.

// Service interface
 type BookService interface {
     GetBook(id string) (*Book, error)
 }

// Mock for testing
 type MockBookService struct {
     GetBookFunc func(id string) (*Book, error)
 }

 func (m *MockBookService) GetBook(id string) (*Book, error) {
     return m.GetBookFunc(id)
 }

This approach allows quick adaptation to contract changes without a complete overhaul of the code.