What is well-tested code like? At least 3 criteria. And what is strong coupling and what are its disadvantages? Why is too weak coupling bad?

Well-tested code has the following criteria:

1. Modularity — code is divided into small, independent components that can be tested separately.
2. Absence of side effects — functions and methods do not depend on external state and do not change it unpredictably.
3. Clearly defined interfaces — input and output data are clear, making testing easier.

Strong coupling — when modules depend heavily on each other, for example, directly using internal details of neighboring components. Downsides:

• Difficult to change one module without affecting others.
• Hard to write modular tests, as many setups and mocks are required.

Too weak coupling — when modules hardly interact, which can lead to:

• Redundancy of code and duplication of logic.
• Difficulties in system integration and coordination.

The optimal level of coupling is a balance where modules are sufficiently independent for testing and maintenance, yet interact effectively to solve the overall task.