Answer:
Because test-first development gives a better and clearer relationship between the programmer's code requirements and the computer system requirements.
It gives the programmer a better understanding of the standards required to write to write test for the computer system.
Potential difficulties
(1) some test-first developments are difficult to write step wise.
(2) some programmers don't give more importance to the testing.
(3) It requires additional time and cost for its effective implementation.
Explanation: Test-first development is a software development methods where the programmer is expected to test the program as it is being developed to ensure that all possible errors or threats to the successful use of the system is guaranteed.
Test-first development gives the developer a better understanding of the software tests or language as it is tested as its development continue, it also has some difficulty as some of them are difficult to write step by step. It also requires adequate time and costs to be effective.