TDD is a development process where tests are written before code to improve software quality. It has two levels: acceptance TDD which writes tests for requirements and developer TDD which writes unit tests for detailed design. The goals of TDD are to have confidence in changes through frequent testing, reduce bugs in final delivery, and produce well-designed code. Problems can occur if requirements change and tests are not maintained, or if programmers think TDD wastes time rather than preventing bugs long-term.

1. TEST DRIVEN DEVELOPMENT
Main reason to follow TDD
TDD is the art of fearless Programming by Improving Software Quality {internal and external quality}.
External quality characteristics are those parts of a product that face its end users,where internal quality
characteristics are those that do not.
External qualityFeatures:
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Functionality
Reliability
Usability
Efficiency
Maintainability
Portability
Internal qualityFeatures:
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Effectiveness
Productivity
Safety
Customer Satisfaction
What is Test Driven Development?
TDD is the process where we write a test first then we write code to make the test pass. Then we find the
best possible design for what we have.
There are two levels of TDD
1. Acceptance TDD (ATDD)
With ATDD you write a single acceptance test or behavioral specification depending on your
preferred terminology, and then just enough production functionality/code to fulfill that test. The
goal of ATDD is to specify detailed, executable requirements for your solution on a just in time
(JIT) basis. ATDD is also called Behavior Driven Development (BDD). Acceptance tests are
indicators of the completion of a requirement or feature. When all acceptance tests for a
requirement or feature are passing, you know you’re done.

2. 2. Developer TDD
With developer TDD you write a single developer test, sometimes inaccurately referred to as
aUnit Test, and then just enough production code to fulfill that test. The goal of developer TDD
is to specify a detailed, executable design for your solution on a JIT basis. Developer TDD is
often simply called TDD.
TDD and acceptance TDD often go hand in hand. On the system level, we run our development process
with acceptance TDD; and inside the implementation step of each feature; we employ TDD
What are the goals of TDD?
Test a little and build a little gives confidence. Reduce the effort of final delivery.
Well-written code
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Good design
A balanced division of responsibilities
Without duplication (clones)
Smooth evolution
Maintainability
ATDD goals
Acceptance TDD helps us keep our product’s external quality on track by giving it the correct features
and functionality. The system should meet what the customer actually need
What are the problems of TDD?
1. It became a difficulttask when requirements changes and unit tests are not done as best
practices (maintainable, readable, and trustworthy).Any little change in our code broke them, even
though the code was working fine. This is the impotent reason programmers ended up
and throwing out most of the tests.
2. I don’t have time to do TDD: some programmers think it’s just a waste of time because they don’t
want to fix bugs, create test cases, figure out what the code is supposed to do and re-factor the
code,etc.
Solution: Think long term