Software Design, Modularity, and Testing
Building maintainable systems
Modularity and separation of concerns
Good software design divides a system into pieces with clear responsibilities. Each module should do one job well and interact with others through simple interfaces. This reduces coupling and makes code easier to understand, test, and change.
Tight vs. loose coupling
Tight coupling
- Modules depend heavily on each other's internal details
- Changes in one part can break many others
Loose coupling
- Modules communicate through stable interfaces
- Changes are easier to isolate and manage
Testing levels
Unit tests verify small pieces in isolation, integration tests check that components work together, and end-to-end tests validate the full user flow. A healthy test strategy uses all three at different points in the development cycle.
What is the main purpose of unit testing?
Unit tests focus on individual functions or modules.
Correct answer: To verify a small piece of code in isolation
Why is loose coupling beneficial?
Clear interfaces reduce the impact of change.
Correct answer: It makes systems easier to modify and test because components depend less on internal details.
Debugging mindset
When something breaks, form a hypothesis, isolate the cause, reproduce the issue reliably, and change one thing at a time.
A practical debugging routine
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Step 1: Reproduce the bug consistently.
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Step 2: Reduce the problem to the smallest failing case.
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Step 3: Inspect inputs, assumptions, and recent changes.
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Step 4: Add logging or breakpoints to observe state.
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Step 5: Fix the root cause and retest thoroughly.
Which test checks that multiple components work together?
Integration tests verify interactions between modules.
Correct answer: Integration test
What is one sign of good code organization?
Clarity of responsibility helps maintainability.
Correct answer: Each module has a clear responsibility and a simple interface.