测试需要用户 input() 的 Python 函数

Question

I want to test the following function:

def get_inputs():
    str_from_user = input()
    list_of_marks = []
    while str_from_user != "exit":
        list_of_marks.append('!')
        str_from_user = input()
    return list_of_marks

is there a way to test multiple scenarios? something like this (but only that works):

def test_get_inputs():
    assert get_inputs(){"hey", "coco", "milo", "exit"} == "!!!"
    assert get_inputs(){"exit"} == ""
    assert get_inputs(){"horses have long faces", "exit} == "!"

Answer 1

There is no obvious way to test your function as it is currently written, because you are reading from standard input. This is a side effect that makes your function non- pure and hard to test. In other words, the input comes from outside your program, so you do not have control over it.

You should rewrite your function in a way that makes it easy to provide input and check output within the program. You can do this passing a function to use as a way to get input instead of always using input() . Then, for testing, you can create a simple iterator object over a list of known inputs and pass its __next__ method as input function.

Here's an example of how this could be done:

def get_inputs(input_function):
    str_from_user = input_function()
    list_of_marks = []
    while str_from_user != "exit":
        list_of_marks.append('!')
        str_from_user = input_function()
    return list_of_marks

def test_get_inputs():
    input_func_one   = iter(["hey", "coco", "milo", "exit"]).__next__
    input_func_two   = iter(["exit"]).__next__
    input_func_three = iter(["horses have long faces", "exit"]).__next__
    assert get_inputs(input_func_one) == ['!', '!', '!']
    assert get_inputs(input_func_two) == []
    assert get_inputs(input_func_three) == ['!']

Another option, as suggested by @chepner in the above comments, would be to pass the function a file-like object, which can be easily mocked using the io module with either BytesIO or StringIO . Take care in this case though because input() strips the trailing newline, but StringIO.readline() does not.

from io import StringIO

def get_inputs(input_file):
    str_from_user = input_file.readline().rstrip()
    list_of_marks = []
    while str_from_user != "exit":
        list_of_marks.append('!')
        str_from_user = input_file.readline().rstrip()
    return list_of_marks

def test_get_inputs():
    assert get_inputs(StringIO("hey\ncoco\nmilo\nexit\n")) == ['!', '!', '!']
    assert get_inputs(StringIO("exit\n")) == []
    assert get_inputs(StringIO("horses have long faces\nexit\n")) == ['!']

You could also adapt the first case (passing an input function) to work with StringIO by simply passing StringIO("...").readline as function.

---

Not what you have a function that is easily testable, you can write a simple wrapper that uses the function and works with standard input instead:

# If using an input function
def get_inputs_from_stdin():
    return get_inputs(input)

# If using a file-like object
import sys

def get_inputs_from_stdin():
    return get_inputs(sys.stdin)