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Indeterminate functions

Learning objectives

  • practice writing tests for indeterminate functions within a formal testing framework
For teachers

Prerequisites are:

  • Learners have .

Teaching goals are:

  • Learners .

Teaching form used:

  • .

Lesson plan:

  • 5 mins: prior knowledge
  • When do you trust your code?
  • When do you trust code written by others?

  • How do you convince other developers of a bug?

  • 5 mins: presentation

  • 10 mins: demonstration is_zero
  • 25 mins: challenge
  • 10 mins: feedback

Testing indeterministic functions

Functions that do not always return the same values.

def flip_coin():
    """Produce a random boolean."""
    return random.randint(0, 1) > 0

How to test these?

Randomness

A Random Number Generator ('RNG') produces the same random values after setting the same RNG seed.

import random
random.seed(5)
assert flip_coin()
random.seed(2)
assert not flip_coin()

Exercises

Exercise 1: first attempt

Learning objectives
  • practice writing tests for indeterminate functions within a formal testing framework

In pairs, develop a function using TDD using the unittest framework.

The function is a function which returns the result of a dice throw: a random integer value from 1 to and including 6.

The function

  • Function name: get_dice_throw_value_[names], for example, get_dice_throw_value_anna_and_sven
  • Output:
    • Returns a random integer value from 1 to and including 6.

Social

  • Ping-Pong Pair programming
  • Discuss how and when to switch roles first!
  • Decide who is the first driver, e.g. the person with first name first in alphabet
  • Try to be an exemplary duo

Technical

  • Create a topic branch for your pair. Branch of from develop
  • Work within scaffolding of the learners project
    • Functions are in src/[package_name]/. Call the file utils_[names].py, e.g. utils_anna_and_sven.py
    • Tests are in tests/. Call the file test_utils_[names].py, e.g. test_utils_anna_and_sven.py
  • When done, create a Pull Request to develop. Do not merge!

Exercise 2: second attempt

Learning objectives
  • practice writing tests for indeterminate functions within a formal testing framework

In pairs, develop an indeterminate function using TDD using the unittest framework.

Use the same setup as exercise 1.

However, decide upon an interesting function at your estimated level. When disagreeing: pick the easiest function.

If needed, this function is suggested:

The function

  • Function name: get_lottery_values_[names], for example, get_lottery_values_anna_and_sven
  • Input: the highest value that can be drawn, e.g. 45, which is common in lottry gameshttps://en.wikipedia.org/wiki/List_of_six-number_lottery_games
  • Output: Returns a list of six random numbers, in range [1, highest_value] (i.e. including one and the highest value that can be drawn). Each number must be unique. The numbers need not to be sorted. Assuming a highest value of 45, them:
    • Valid examples: [1, 2, 3, 4, 5, 6], [6, 5, 4, 3, 2, 1]
    • Invalid examples: [1, 1, 1, 1, 1, 1] (due to duplicates), [1, 2, 3, 4, 5, 46] (last value is heigher than 45),
  • If the input is not one integer that is at least 6, a TypeError is raised.