Examples of unittests used in my small programme

Question

Hey, I have tough time working on this.
I need to add 3 unittest's to my code, nothing too complicated, just need to use unittest and check something in this code, like is it possible to count NPV (so it's checking if there are 9 values in my .csv file? not sure how does testing work...) ?
I have no idea how to implement it to my code and I can't understand examples from the internet. Would love to see them on my code, maybe then I could finally get it.
Can anyone of you help me with this?
My code is counting NPV from .csv file (here's a link to it: https://www.justbeamit.com/w8iuk)
Code:
---
from pandas import read_csv
from numpy import npv
def counting_npv():
for index, row in fund.iterrows():
row = row.tolist()
np_list.append(npv(row[1], row[2:]))
prjN = row[0]
print("NPV for project no. {}: PLN {:,.2f}".format(prjN, np_list[index]))
fund = read_csv("inwestycje.csv", delimiter=',')
funds = [tuple(x) for x in fund.values]
np_list = []
counting_npv()
maxnpv = (np_list.index(max(np_list)))+1
print ("Best project: {}.".format(maxnpv))
---
Thank you in advance!
Cheers.

Answer 1

The way I'd do it is create 3 files with answers you know. Create a function to process one of those files and verify your counting is doing the correct thing for it's content. Repeat this for the other 2 files. You could write the fixed data of the file in those functions.
You could use: os.path.isfile("inwestycje.csv") to see if a user file exists. If yes, process it. If no, run your test functions.