However, TDD encourages – ideally – a style of programming where 100% branch coverage is likely to mean the program is correct. That's part of the idea of the

However, TDD encourages – ideally – a style of programming where 100% branch coverage is likely to mean the program is correct. That's part of the idea of the "unit" in "unit test." You decompose the program into units for which correctness is relatively simple – and testable. How to do this properly is not obvious, and for teams on which TDD is imposed without this understanding, it will all become a bizarre and useless ideology. When it is understood, the resulting program will have properties that resemble those of purely functional programs, especially composability and correctness.