It’s like having a personal stylist for your test doubles but instead of picking out their wardrobe, it picks out their API and call signature.

So what exactly is auto-speccing? Well, let me break it down for you in plain English (because who needs fancy jargon anyway). Basically, when you create a mock object using the “create_autospec()” function from unittest.mock module, it automatically copies the attributes and methods of another object that you specify as its spec.

Here’s an example: let’s say you have a function called `my_function` that takes three arguments (a, b, c) and returns “fishy”. You want to test this function using mock objects instead of actual data. So you create a mock object for the input parameters and another one for the output value like so:

# Importing necessary modules
from unittest.mock import Mock, create_autospec

# Defining a function with three arguments
def my_function(a, b, c):
    pass

# Creating mock objects for the input parameters
input_args = [Mock(), Mock(), Mock()]

# Creating a mock object for the output value
output_value = 'fishy'

# Creating a mock function using create_autospec
# This ensures that the mock function has the same signature as the original function
mock_my_function = create_autospec(my_function)

# Setting the return value of the mock function to be the output value
mock_my_function.return_value = output_value

Now, when you call `mock_my_function()` with the input arguments that you specified earlier (i.e., `input_args[0]`, `input_args[1]`, and `input_args[2]`), it will return “fishy”. But wait! There’s more!

If you call `mock_my_function()` with the wrong number of arguments, or if any of those arguments are not mocks themselves (i.e., they have a different API than what was specified in your mock object), it will raise a TypeError. This is because auto-speccing also checks for correct call signatures when creating mock objects.

It’s like having a personal stylist who knows exactly what API and call signature will make them look their best in any situation. And the best part? You don’t even need to know how to sew or style just let auto-speccing do all the work for you!