How to mock nested functions?

Question

The mocking library I use is ... mock.

I came across this \"mock nested functions\" problem when I tried to write test case for a function(legacy code).

This

Answer 1

One option is to change your function so that it optionally accepts the function to call e.g. if you have:

def fn_to_test():
  def inner_fn():
    return 1
  return inner_fn() + 3

Change it to:

def fn_to_test( inner_fn = null )
  def inner_fn_orig():
    return 1
  if inner_fn==null:
    inner_fn = inner_fn_orig
  return fn() + 3

Then "real" uses will get the right inner function, and in your tests you can provide your own.

fn_to_test() # calls the real inner function
def my_inner_fn():
  return 3
fn_to_test( inner_fn=my_inner_fn ) # calls the new version

You could also do this:

def fn_to_test():
  def inner_fn_orign():
    return 1
  inner_fn = inner_fn_orig
  try:
    inner_fn = fn_to_test.inner_fn
  excecpt AttributeError:
    pass
  return inner_fn() + 3

This way you just define the override:

fn_to_test() # calls the real inner function
def my_inner_fn():
  return 3
fn_to_test.inner_fn = my_inner_fn
fn_to_test() # calls the new version