System Design & Testing Phases

System Design

1. High-Level Design (HLD) vs Low-Level Design (LLD)

• High-Level Design (HLD): Focuses on the overall architecture of the system. It defines the main modules, databases, and how they interact with each other (the 'Big Picture').
• Low-Level Design (LLD): Focuses on the internal logic of each specific module. It details the exact algorithms, data structures, and classes that the programmers will write.

2. Cohesion and Coupling (Important Concepts)

• Cohesion (Should be HIGH): Refers to how closely related the functions within a single module are. A highly cohesive module does exactly ONE job very well.
• Coupling (Should be LOW): Refers to how much different modules depend on each other. If modules are tightly coupled, changing one module will break the others. We want loose coupling so modules can be updated independently.

Software Testing

1. Testing Methods

• Black Box Testing: The tester only knows the inputs and expected outputs. They do NOT look at the internal code. (Testing the functionality).
• White Box Testing: The tester knows the internal logic and inspects the actual source code to ensure all paths and loops work correctly.

2. Levels of Testing

1. Unit Testing: Testing individual, isolated components or functions of the code. Usually done by the developers themselves.
2. Integration Testing: Combining the individually tested units and testing them together to ensure they communicate correctly.
3. System Testing: Testing the entire, fully assembled software system as a whole to verify it meets the overall SRS requirements.
4. Acceptance Testing: The final phase. The actual end-users or clients test the software in a real-world environment to decide if they 'accept' it before it goes live. (Alpha and Beta testing are types of Acceptance Testing).