TDD¶

Learning objectives

Understand what TDD is
Understand why TDD is important
Practice TDD

For teachers

Prerequisites are:

Learners have practiced pair programming
Learners can do the git basic workflow on master

Teaching goals are:

Learners understand what TDD is
Learners understand why TDD is important
Learners have done multiple TDD cycles

Teaching form used:

Pair programming
master branch

Prior knowledge questions:

How do you grow/develop your code?
How do others grow/develop their code?
Why would it be important to have a formal way to grow/develop your code?

Lesson plan:

gantt
  title Lesson plan TDD 1
  dateFormat X
  axisFormat %s
  Pair programming: done, 0, 30
  Theory: extra, 30, 45

gantt
  title Lesson plan TDD 2
  dateFormat X
  axisFormat %s
  Exercise 1: crit, exercise_1, 0, 20s
  Feedback 1: feedback_1, after exercise_1, 10s
  Retrospect: crit, 30, 15s

Introduction¶

Test-driven development (TDD) is a systematic way to grow code, used in academia and industry. It works [Martin, 2011]!

A TDD developer

The TDD cycle

The TDD cycles end when you cannot break your function anymore [Beck, 2022][Langr, 2013].

Advantages of TDD are:

TDD makes developers more productive [Erdogmus & Morisio, 2005]
TDD increases quality of the code [Erdogmus & Morisio, 2005][Alkaoud & Walcott, 2018][Janzen & Saiedian, 2006]
There are plenty of costly programming mistakes documented!
TDD helps shape the project architecture [Mayr, 2005]
TDD helps better modularisation [Madeyski et al., 2010]

Developers do really do this [Beck, 2022][Langr, 2013], even though TDD takes longer (but note [study I cannot find]):

Study	Extra time	Effect
[George & Williams, 2004]	16%	18% more black-box tests pass
[Bhat & Nagappan, 2006]	15%	2x higher code quality
[Nagappan et al., 2008]	15-35%	40%-90% less defects

We will discuss formal testing later, but now note that testing is not about finding bugs [Thomas & Hunt, 2019, tip 66], instead a test is the first user of your code [Thomas & Hunt, 2019, tip 67].

Exercises¶

Technical rules

Use the GitHub repository for the learners of this course,
Work on the main branch
Work in a file called learners/[your_name]/[class_name].py, where [your_name] is the person with first name first in alphabet
Zen Of Python: 'Errors should never pass silently'

Social rules

Ping-Pong Pair programming
Discuss how and when to switch roles first!
Person with first name first in alphabet starts
Try to be an exemplary duo

Exercise 0: `is_zero`¶

Learning objectives

First practice of TDD by re-doing a function that has been developed

Develop the function is_zero with the technical and social rules showed at 'Exercises'.

is_zero

Function name: is_zero
Output:
Returns True if the input is zero
Returns False if the input is not zero
Gives an error when the input is not a number

Answer

Note that the practice of TDD is the goal of the exercise, not the exact outcome.

Here is a possible solution:

def is_zero(x):
    """Determines if the input is one integer that is zero"""
    if not isinstance(x, int):
        raise TypeError("'x' must be of type int")
    if x == 0:
        return True
    return False

assert is_zero.__doc__
assert is_zero(0)
assert not is_zero(1)

has_thrown = False
try:
    is_zero("nonsense")
except TypeError:
    has_thrown = True
assert has_thrown

Need a video?

Here are two videos that show how to develop is_zero for Python and R:

Python video for 'is_zero', from 3:02
R video for 'is_one'

Exercise 1: `is_even`¶

Learning objectives

Practice of TDD by developing a slightly more complicated function

Develop a function called is_even:

is_even

Function name: is_even
Output:
Returns True if the input is even
Returns False if the input is not even
Gives an error when the input is not a number

Answer

Note that the practice of TDD is the goal of the exercise, not the exact outcome.

Here is a possible solution:

def is_even(x):
    if not isinstance(x, int):
        raise TypeError("'x' must be of type int")
    """Determine if the input is one integer that is even"""
    return x % 2 == 0

assert is_even.__doc__
assert is_even(2)
assert not is_even(1)

# 'is_even("nonsense")' throws a TypeError 
# because of the modulo operator

has_thrown = False
try:
    is_even(0.0)
except TypeError:
    has_thrown = True
assert has_thrown

Need a video?

Here are a videos that show how to develop is_even for Python:

YouTube

Exercise 2: `is_odd`¶

Learning objectives

Practice of TDD by developing a slightly more complicated function

Develop a function called is_odd:

is_odd

Function name: is_odd
Output:
Returns True if the input is odd
Returns False if the input is not odd
Gives an error when the input is not a number

Consider using the is_even function.

Answer

Note that the practice of TDD is the goal of the exercise, not the exact outcome.

Here is a possible solution:

def is_even(x):
    """Determine if the input is one integer that is even"""
    if not isinstance(x, int):
        raise TypeError("'x' must be of type int")
    return x % 2 == 0

assert is_even.__doc__
assert is_even(2)
assert not is_even(1)

# 'is_even("nonsense")' throws a TypeError 
# because of the modulo operator

has_thrown = False
try:
    is_even(0.0)
except TypeError:
    has_thrown = True
assert has_thrown

def is_odd(x):
    """Determine if the input is one integer that is odd"""
    return not is_even(x)

assert is_odd.__doc__
assert is_odd(1)

# Already passes, consider not putting it in
# assert not is_odd(2)

# Already passes, consider not putting it in
# has_thrown = False
# try:
#     is_odd(0.0)
# except TypeError:
#     has_thrown = True
# assert has_thrown

Need a video?

Here is a videos that show how to develop is_odd for Python:

YouTube

Exercise 3: `is_probability`¶

Learning objectives

Practice of TDD by developing a slightly more complicated function

Develop a function called is_probability.

is_probability

Function name: is_probability
Output:
Returns True if the input is in the range [0.0, 1.0], that is from (and including) zero to (and including) one.
Returns False if the input is not a probability
Gives an error when the input is not one number

Answer

Note that the practice of TDD is the goal of the exercise, not the exact outcome.

Here is a possible solution:

def is_probability(x):
    """Determine if `x` is a probability.

    Determine if `x` is a probability,
    i.e. a value between 0.0 and 1.0, including both 0.0 and 1.0.
    If `x` is not a floating point number, a `TypeError` is raised.

    Returns `True` if `x` is a probability
    """
    if not isinstance(x, float):
        msg = "'number' must be a floating point number. "
        raise TypeError(
            msg,
            "Actual type of 'number': ", type(x),
        )
    min_probability = 0.0
    max_probability = 1.0
    return x >= min_probability and x <= max_probability

Exercise 4: `is_prime`¶

Learning objectives

Practice of TDD by developing a slightly more complicated function

Develop a function called is_prime.

is_prime

Function name: is_prime
Output:
Returns True if the input is a prime number.
Returns False if the input is not a prime number.
Gives an error when the input is not one number

Need a video?

Here is a videos that show how to develop is_prime for Python:

YouTube

Exercise 5: practice¶

Learning objectives

Practice of TDD

Go to the Programming Formalisms page 'functions to practice TDD'. Pick a function at your level.

Technical rules

Use the shared GitHub repository for the learners of this course
Pick a branching model. When unsure, work on main
Use no testing framework or unittest. When unsure, use no testing frameworks
No testing framework: work in a file called learners/[your_names]/[function_name].py, e.g. learners/anna_and_bertil/is_zero.py
unittest framework: work in a file in the src folder (e.g. src/anna_and_bertil_utils.py), write the tests in the tests folder, e.g. tests/test_anna_and_bertil_utils.py

Social rules

Ping-Pong Pair programming
Discuss how and when to switch roles first
Person with first name first in alphabet starts
Try to be an exemplary duo

Signs you are doing great

In an online course:

A good pair has the driver sharing his/her screen
In a good pair, both people talk a lot
A good pair switches roles regularly
A good pair has a lot of commits

Conclusion¶

This session, we wrote unit tests
It is only those your boss may read
The literature assumes a responsible programmer writes tests, in C++ [Stroustrup & Sutter, 2017], R [Wickham, 2019] and Python [PEP 8]

Discussion¶

We only test manually
We only test on our own computer
We are not sure if our functions are tested completely
We do not test the code for style
We should consider using a testing framework

Videos¶

Title	Length	YouTube
TDD 1/3: TDD	5 mins	YouTube
TDD 2/3: `is_zero`	16 mins	YouTube
TDD 3/3: Introduce `is_even`	3 mins	YouTube
Solution `is_even`	12 mins	YouTube
TDD 2: introduce `is_odd`	7 mins	YouTube
Solution `is_odd`	7 mins	YouTube
TDD 3: TDD bottom line	4 mins	YouTube
Solution `is_prime`	9 mins	YouTube

References¶

[Alkaoud & Walcott, 2018] Alkaoud, Hessah, and Kristen R. Walcott. "Quality metrics of test suites in test-driven designed applications." International Journal of Software Engineering Applications (IJSEA) 2018 (2018).

[Beck, 2022] Beck, Kent. Test driven development: By example. Addison-Wesley Professional, 2022.
[Bhat & Nagappan, 2006] Bhat, Thirumalesh, and Nachiappan Nagappan. "Evaluating the efficacy of test-driven development: industrial case studies." Proceedings of the 2006 ACM/IEEE international symposium on Empirical software engineering. 2006.
[Erdogmus & Morisio, 2005] Erdogmus, Hakan, Maurizio Morisio, and Marco Torchiano. "On the effectiveness of the test-first approach to programming." IEEE Transactions on software Engineering 31.3 (2005): 226-237.
[George & Williams, 2004] George, Boby, and Laurie Williams. "A structured experiment of test-driven development." Information and software Technology 46.5 (2004): 337-342.
[Janzen & Saiedian, 2006] Janzen, David S., and Hossein Saiedian. "Test-driven learning: intrinsic integration of testing into the CS/SE curriculum." Acm Sigcse Bulletin 38.1 (2006): 254-258.

[Langr, 2013] Langr, Jeff. Better, Code, and Sleep Better. "Modern C++ Programming with Test-Driven Development." (2013).
[Madeyski et al., 2010] Madeyski, Lech, and Gestión de sistemas de información. Test-driven development: An empirical evaluation of agile practice. Heidelberg: Springer, 2010.

[Martin, 2011] Martin, Robert C. The clean coder: a code of conduct for professional programmers. Pearson Education, 2011.
[Mayr, 2005] Mayr, Herwig. Projekt Engineering: Ingenieurmäßige Softwareentwicklung in Projektgruppen. Hanser Verlag, 2005.
[Nagappan et al., 2008] Nagappan, Nachiappan, et al. "Realizing quality improvement through test driven development: results and experiences of four industrial teams." Empirical Software Engineering 13 (2008): 289-302.
[PEP 8] Van Rossum, Guido, Barry Warsaw, and Nick Coghlan. "PEP 8–style guide for python code." Python. org 1565 (2001): 28.
[Stroustrup & Sutter, 2017] Stroustrup, Bjarne, and Herb Sutter. "C++ Core Guidelines (2017)." URL http://isocpp. github. io/CppCoreGuidelines/CppCoreGuidelines.(Cited on pages 100 and 103) (2015).
[study I cannot find] in one of the classics, there was a bar chart that showed developers write functions such as is_prime with and without TDD and showed that TDD was twice as fast. TODO: find this reference

[Thomas & Hunt, 2019] Thomas, David, and Andrew Hunt. The Pragmatic Programmer: your journey to mastery. Addison-Wesley Professional, 2019.
[Wickham, 2019] Wickham, Hadley. Advanced R. Chapman and Hall/CRC, 2019.

[Zen of Python] Zen Of Python: 'Errors should never pass silently'

TDD¶

Introduction¶

Exercises¶

Exercise 0: is_zero¶

Exercise 1: is_even¶

Exercise 2: is_odd¶

Exercise 3: is_probability¶

Exercise 4: is_prime¶

Exercise 5: practice¶

Conclusion¶

Discussion¶

Videos¶

References¶

Exercise 0: `is_zero`¶

Exercise 1: `is_even`¶

Exercise 2: `is_odd`¶

Exercise 3: `is_probability`¶

Exercise 4: `is_prime`¶