test driven development

Author: louisrli

module5-testing/r2.1-testdriven-development/README.md

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+# Test-driven Development
+
+**Test-driven development** (TDD) is a process where developers write the tests first,
+**before** writing the code. As we saw in the last section, the tests alone can
+be sufficient for specifying the behavior of the function.
+
+Even to modify existing code, a test would be written first under this
+philosophy. For example, if you had an `if` statement in your code already, but
+you wanted to add an `else` branch, under TDD, you would first write a test for
+that `else` branch, and then write the actual code. As mentioned before, at the
+highest levels of testing, a mistake in any line of code should be caught, and
+TDD facilitates this.
+
+## Why TDD?
+
+First, TDD requires the developer to first think
+about the behavior of the tested code and how it will be used, rather than
+rushing head-first into writing the code. Perhaps you may have experienced
+writing code and realizing later that the code you wrote was not quite what you
+needed. When you think carefully first about the behavior of the code as in TDD,
+this situation is often avoided.
+
+Second, as developers must write tests with every code, TDD requires developers
+to write tests and puts developers in the habit of writing tests, which is
+generally healthy for the robustness of a codebase. If TDD was not present,
+depending on the company, developers may be less strict about writing tests.
+
+## Is TDD used in the real world?
+Many companies do adopt TDD, although in practice, this is a minority of
+companies. TDD is far from a perfect philosophy: it does not guarantee good test
+coverage and it may even encourage developers to write sloppier tests so that
+they can simply start coding faster.
+
+However, as with all things
+in life, understanding the perspective of TDD is still extremely useful.
+But as all things in life, learning different perspectives is useful.
+TDD is on the very rigorous end of the role of testing in
+development. In reality, you will probably end up somewhere in between --
+perhaps sometimes you will think about the tests first, or you will think in
+your head about what will be tested, even though you may not be required to
+actually write the tests as you would in TDD.
+
+The reason that understanding or trying test-driven development is helpful is
+because even if you do not work at a company that adopts test-driven
+development, it will encourage you to think about success and failure cases
+while you write your code. **This is a crucial part of the programmer's
+mindset.** As you become a more experienced programmer, you will try to predict
+issues; test-driven development aids greatly with this mindset, since it
+encourages you to write the test and think about these scenarios before writing
+the code.