Whack-A-Mole Debugging

Thank you for helping with https://github.com/UCLA-CS-35L/whack-a-mole! Now, all the moles have been whacked, and I have correct implementations of all of my algorithms in src/algo.py.

It's time to use my algorithms library! I'm trying to write a vending machine application. However, it's got some problems.

Your goal:

1. Investigating symptoms to reproduce the bug
2. Locating the faulty code
3. Determining the root cause of the bug
4. Implementing and verifying a fix

Setup

As a reminder, see https://github.com/UCLA-CS-35L/whack-a-mole for setup.

It may be helpful to do pipenv shell and run the commands from within this shell.

Using the Vending Machine

The source code is found in src/vending_machine.py. Notice that it imports some functions from algo. To see instruction on how to run the application, use python3 src/vending_machine.py --help.

The vending machine CSV file (the file argument) is provided in machine.csv. The contents of this file are reproduced below (space added):

row, column, name,      price
1,   A,      Chips,     120
1,   B,      Soda,      150
1,   C,      Candy,     80
2,   A,      Gum,       50
2,   B,      Cookie,    100
2,   C,      Chocolate, 200

• row and column encode the cell where it is in the machine
• name is the name of the item
• price is the price of the item

An example invocation would be as follows:

$ python3 run src/vending_machine.py machine.csv price Chips
Price of Chips is $120

This is correct as the price of the chips in the table is $120.

Debugging

As a reminder, your goal is to fix the bugs!

debugging step	how
Investigating symptoms to reproduce the bug	partially complete; see tests/test_vending_machine.py
Locating the faulty code	adding breakpoints and running tests in debug mode
Determining the root cause of the bug	describing what is logically wrong in the code
Implementing and verifying a fix	edit the source code in src/vending_machine.py and rerun tests

Here's a step-by-step checklist to do this activity:

• make a fork of this repository

• find some buggy behavior: this has been done for you!

  • tests/test_vending_machine.py is provided to check some potential problems
  • make sure you can describe what each test does!

• run all the tests

• for each failing test, go to the corresponding function and add a breakpoint somewhere

• rerun failing tests in debug mode

• identify at what point are the variables' values are no longer correct

• note down a potential fix at each point

• determine the root cause

• consider how src/vending_machine.py might be refactored to address multiple fixes at once

• run all the tests

  • ensure your fixes didn't break any existing passing tests!

• push to your fork and ensure the GitHub CI passes (green check mark)

  • you may need to enable GitHub CI in the "Actions" tab
  • optionally, submit a pull request with a fix!