Simulate shell input for regression test

Question

I'm trying to setup regression testing for an app before refactoring. The function is one long mess, starting with parsing user input and performing numerous operations before giving an output. I want to test expected values given a set of inputs (including defaults), but am not sure how to simulate a user's shell input inside a test module. Here's an example of how input is taken at the start of the file:

def function():
    parser = ArgumentParser()
    parser.add_argument("-a", "--term-a", type=float, default=0.5, help="a term relevant to output")
    parser.add_argument("-b", "--term-b", type=float, default=0.05, help="a term relevant to output")
    parser.add_argument("-c", "--term-c", type=int, default=2, help="a term relevant to output")
    parser.add_argument("-f", "--file-a", type=str, required=True,
                     help="Input file required for output")
    args = parser.parse_args()

    ...

Possible duplicate: [how to pass command line argument from pytest to code](https://stackoverflow.com/q/54071312/2650249) — hoefling, Oct 26 '20 at 23:27

CryptoFool · Accepted Answer · 2020-10-26T22:59:46.857

2

parse_args() can take an arbitrary list of arguments rather than reading from sys.argv, So just pass it the arguments you want to simulate a user having passed in, like this:

parser.parse_args(['--term-a', '7.5', '--file-a', '/tmp/data.txt'])

You could refactor your function, or just have it take an optional parameter, like this:

def function(args=None):
    parser = ArgumentParser()
    parser.add_argument("-a", "--term-a", type=float, default=0.5, help="a term relevant to output")
    parser.add_argument("-b", "--term-b", type=float, default=0.05, help="a term relevant to output")
    parser.add_argument("-c", "--term-c", type=int, default=2, help="a term relevant to output")
    parser.add_argument("-f", "--file-a", type=str, required=True,
                     help="Input file required for output")
    args = parser.parse_args(args)

so it would still act like it does now, but you could also pass it canned test data, like this:

function(['--term-a', '7.5', '--file-a', '/tmp/data.txt'])

edited Oct 26 '20 at 22:59

answered Oct 26 '20 at 22:47

CryptoFool

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Ah I see, thanks. If I were to refactor and pull out the parser as a separate function say “function2”, could the test referencing “function([canned parameters])” stay unchanged? So the test gives “function” a set of parameters, and “function” calls the newly refactored “function2” which and passes said set of parameters. Would both “function” and “function2” need ‘args=None’? – AJG Oct 27 '20 at 01:12
what was `function` becomes `function2`, right? Then `function` contains just the equivalent of that one line of code I gave you above, yes? - so the test can just call `function()`. – CryptoFool Oct 27 '20 at 01:15
Function would contain all the other content involved in generating the output (the “...” in the code snippet), fuction2 would contain the code above the ellipsis, so just the parsing. – AJG Oct 27 '20 at 01:20

Simulate shell input for regression test

1 Answers1