Beginners, in the sense in which I’m using the word, don’t use test runners.
I deliberately didn’t call them “unit tests”. The pattern for the very simplest tests is
if __name__=="__main__":
print(f(1,2)) # should be 3.0
or even
if __name__=="__main__":
df = pd.read_csv(file_path, engine=“python”, comment=“%”)
print(df.head(3))
As for how many beginners actually test the components of their code: not enough 
Just looking at Why does this graph still show two outliers? as an example, from last week in the Python Help section, if this guy had tested the components of his code, he could have asked a better question.
That post incidentally also demonstrates the cargo-culting with if __name__=="__main__": main(). The code didn’t need it, and using the paradigm probably made it harder on the beginning python user to understand what python is doing, why and how.