What is the difference between testing monolithic backend and testing web service architecture?

Testing a monolith focuses on testing a single, large application. The main levels of testing are: component (modular, if code is available), integration (within the monolith and with external dependencies), and system (end-to-end). Tools and approaches are more standard.

Testing web service architectures (e.g., microservices) is more complex and requires a different approach:

• Distributed system: Testing covers the interaction of multiple independent services. Contracts (APIs) between services are important.
• Testing levels:
  • Unit Testing: Testing individual services in isolation.
  • Component Testing: Testing the functionality of a single service with its internal dependencies.
  • Integration Testing: Testing the interaction between two or more services. This is a critical level.
  • End-to-End Testing: End-to-end testing of data flow across multiple services. It can be complex and fragile.
• Types of testing:
  • Contract Testing: Checking API compliance between services.
  • Performance & Load Testing: Testing the performance and scalability of each service and the system as a whole.
  • Resiliency Testing: Testing system resilience to service failures (Chaos Engineering).
• Tools: Specialized tools are used for testing APIs, distributed systems (e.g., for monitoring and tracing).
• Environments: Management of more complex test environments, including multiple deployed services.

Comparison table:

Criterion	Monolithic backend	Web service architecture (Microservices)
System size	Single large application	Multiple small, independent services
Interaction	Within one application, with external dependencies	Between services (over the network), with external dependencies
Main focus	Internal logic, component integration	Service interaction, contracts, fault tolerance
Environment complexity	Relatively low	High (managing multiple deployments)
Key Testing Types	Unit, internal integration, system	Unit, component, inter-service integration, end-to-end, contract, resiliency
Tools	Standard testing frameworks	Specialized for APIs, distributed systems