First Law of TDD

Correct Answer: Write a failing unit test for the function that captures the requirement mismatch

The First Law of Test-Driven Development (TDD) is 'You are not allowed to write any production code unless it is to make a failing unit test pass.' This implies that, in order to address a situation where requirements aren't met, you should first create a failing unit test to reflect the scenario that is failing due to the requirement mismatch. This guides the development of the code necessary to pass the test, fostering simple and effective solutions. Raising a bug and waiting for triage is not the most appropriate approach as per the First Law of TDD, which emphasizes immediate redressal through a unit test. Correcting the function right away is against the First Law of TDD, which mandates failing unit tests before writing code. Deprecating the function to write a new one from scratch doesn't align with TDD principles, which encourage incremental improvement through failing tests and then passing them.

Correct Answer: A team member first writes a failing test for a feature, then produces the minimum amount of code to pass the test

The appropriate application of the Test Driven Development (TDD) First Law is depicted as follows: 'A team member first writes a failing test for a feature, then produces the minimum amount of code to pass the test'. The TDD process starts with a failing test and then writing the least amount of code to make it pass, enabling developers to focus on one small piece of functionality at a time. The scenario where 'A team member writes production code and tests alongside one another' is incorrect as in TDD, tests are written first before production code. The scenario 'A team member writes all the tests and then starts the production code' results in many failing tests simultaneously. This can lead to losing focus on the task at hand and makes it harder to identify issues when they arise. 'A team member writes all the production code and then writes the tests': this is not the TDD approach. In TDD, tests guide the code you write, and so should be written first and pass before any new production code is written.

Correct Answer: Write failing unit test -> Write production code to pass the test -> Refactor

TDD, or Test-Driven Development, is a software development methodology where a failing test case is written first before production code is written to make the test pass, this is why the choice 'Write failing unit test -> Write production code to pass the test -> Refactor' is the correct answer. The other answers provided are not in accordance with the TDD process. Writing production code before writing a failing unit test breaks the first rule of TDD's First Law which states, 'You are not allowed to write any production code unless it is to make a failing unit test pass.' Similarly, the step of refactoring comes last in the TDD process, after the failing test is passing, which is why the choices 'Refactor -> Write production code -> Write failing unit test' and 'Write failing unit test -> Refactor -> Write production code to pass the test' are incorrect.