Less coupling makes code easier to extend and maintain. Tight coupling makes code more rigid and brittle and more likely to break when changes are needed.

Coupling takes different forms: 

• Subclass coupling is dependent on the implementation and hierarchy of the p...

TDD should simplify code, not make it more complicated. If your code becomes harder to read or maintain when you make it testable, you're doing TDD wrong.

You can learn two things:

• You can write decoupled code without dependency injection, and

Unit tests test individual units (modules, functions, classes) in isolation from the rest of the program.

• Generally, units are tested using the public interface of the unit, known as black-box testing. It leads to less brittle tests.
• In white box testing - whe...

Tight coupling has many causes: 

• Mutation vs immutability  
• Side-Effects vs purity/isolated side-effects  
• Responsibility overload vs Do One Thing (DOT)  
• Procedural instructions vs describing s...

A code smell is a surface indication that points to a deeper problem in the system.

Different types of code need different levels (and different kinds) of mocks. Some code exists primarily to facilitate I/O, in which case, there is little to do other than test I/O. Reducing...