CSE 111: Programming with Functions

03 Prove Milestone: Testing and Fixing Functions

Purpose

Prove that you can write a Python program and write and run test functions to help you find and fix mistakes in your program.

Problem Statement

Getting clean water to all buildings in a city is a large and expensive task. Many cities will build an elevated water tank, and install a pump that pushes water up to the tank where the water is stored. In the city, when a thirsty person opens a water faucet, water runs from the tank through pipes to the faucet. Earth’s gravity pulling on the water in the elevated tank pressurizes the water and causes it to spray from the faucet.

A diagram of a city water distribution system that stores water in an elevated tank
A diagram of a city water distribution system that stores water in an elevated tank

Before a city builds a water distribution system, an engineer must design the system and ensure water will flow to all buildings in the city. An engineer must choose the tower height, pipe type, pipe diameter, and pipe path. Engineers use software to help them make these choices and design a working water distribtuion system.

Assignment

Write a Python program that could help an engineer design a water distribution system. During this prove milestone, you will write three program functions and three test functions as described in the Steps section below.

Helpful Documentation

Help from a Tutor

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Steps

Do the following:

  1. Using VS Code, create a new file and save it as water_flow.py
  2. Create another new file, save it as test_water_flow.py, and copy and paste the following import statements into the file. 
    from pytest import approx
import pytest
  3. In your water_flow.py program, write a function named water_column_height that calculates and returns the height of a column of water from a tower height and a tank wall height. The function must have this header: 
    def water_column_height(tower_height, tank_height):

    In your function, use the following formula for calculating the water column height.

    h = t +
    3w
    4
    where
    • h is height of the water column
    • t is the height of the tower
    • w is the height of the walls of the tank that is on top of the tower
  4. In your test_water_flow.py file, write a test function named test_water_column_height. This test function must call water_column_height at least four times to verify that it is working correctly. Use the following numbers in your test function.
    Tower
    Height    		 Tank Wall
    Height    		 Expected Water
    Column Height
    0 0 0
    0 10 7.5
    25 0 25
    48.3 12.8 57.9
  5. In your water_flow.py program, write a function named pressure_gain_from_water_height that calculates and returns the pressure caused by Earth’s gravity pulling on the water stored in an elevated tank. The function must have this header: 
    def pressure_gain_from_water_height(height):

    In your function, use the following formula for calculating pressure caused by Earth’s gravity.

    P =
    ρgh
    1000
    where
    • P is the pressure in kilopascals
    • ρ is the density of water 998.2 ( kilogram / meter3) *Just use # in your calculations
    • g is the acceleration from Earths gravity 9.80665 (meter / second2) *Just use # in your calculations
    • h is the height of the water column in meters
  6. In your test_water_flow.py file, write a test function named test_pressure_gain_from_water_height. This test function must call pressure_gain_from_water_height at least three times to verify that it is working correctly. Use the following numbers in your test function.
    Height Expected
    Pressure    		 approx
    Absolute
    Tolerance
    0 0 0.001
    30.2 295.628 0.001
    50 489.450 0.001
  7. In your water_flow.py program, write a function named pressure_loss_from_pipe that calculates and returns the water pressure lost because of the friction between the water and the walls of a pipe that it flows through. The function must have this header: 
    def pressure_loss_from_pipe(pipe_diameter,
        pipe_length, friction_factor, fluid_velocity):

    In your function, use the following formula for calculating pressure loss from friction within a pipe.

    P =
    − f L ρ v2
    2000 d
    where
    • P is the lost pressure in kilopascals
    • f is the pipe’s friction factor
    • L is the length of the pipe in meters
    • ρ is the density of water 998.2 (kilogram / meter3) *Just use # in your calculations
    • v is the velocity of the water flowing through the pipe in meters / second
    • d is the diameter of the pipe in meters
  8. In your test_water_flow.py file, write a test function named test_pressure_loss_from_pipe . This test function must call pressure_loss_from_pipe at least seven times to verify that it is working correctly. Use the following numbers in your test function.
    Pipe
    Diameter    		 Pipe
    Length    		 Friction
    Factor    		 Fluid
    Velocity    		 Expected
    Pressure
    Loss    		 approx
    Absolute
    Tolerance
    0.048692 0 0.018 1.75 0 0.001
    0.048692 200 0 1.75 0 0.001
    0.048692 200 0.018 0 0 0.001
    0.048692 200 0.018 1.75 -113.008 0.001
    0.048692 200 0.018 1.65 -100.462 0.001
    0.28687 1000 0.013 1.65 -61.576 0.001
    0.28687 1800.75 0.013 1.65 -110.884 0.001
  9. Copy and paste the following code at the bottom of your test_water_flow.py file. 
    # Call the main function that is part of pytest so that the
# computer will execute the test functions in this file.
pytest.main(["-v", "--tb=line", "-rN", __file__])

Testing Procedure

Verify that your functions work correctly by following each step in this procedure:

  1. Run your test_water_flow.py file and ensure that all three of the test functions pass. If any of the test functions don’t pass, there is a mistake in either the program function that you wrote or the test function that you wrote. Read the output from pytest, fix the mistake, and run the test_water_flow.py file again until all the test functions pass. 
    > python test_water_flow.py
======================== test session starts ==========================
platform win32 -- Python 3.11.1, pytest-7.2.1, pluggy-1.0.0 --
rootdir: C:\Users\cse111\week03
collected 3 items
test_water_flow.py::test_water_column_height PASSED              [ 33%]
test_water_flow.py::test_pressure_gain_from_water_height PASSED  [ 66%]
test_water_flow.py::test_pressure_loss_from_pipe PASSED          [100%]
========================= 3 passed in 0.07s ===========================

Ponder

During this assignment, you wrote three program functions named water_column_height, pressure_gain_from_water_height, and pressure_loss_from_pipe. Also, in a separate file, you wrote three test functions. Each of the test functions called one of the program functions multiple times and automatically verified that the value returned from the program function was correct. If you worked as a software developer on a large project with four other software developers, how would test functions help you and the other developers ensure that your program worked correctly?

Submission

On or before the due date, return to Canvas and report your progress on this milestone.

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