how to mock a call to __next__

You need to use MagicMock, not Mock, to have magic methods like __next__ available by default:

>>> from unittest import mock
>>> mock_coroutine = mock.MagicMock()
>>> mock_coroutine.__next__()
<MagicMock name='mock.__next__()' id='4464126552'>
   >>> mock_coroutine.__next__.assert_called_with()

So, alternatively, you could still use the regular Mock object, but then you need to explicitly add that attribute:

>>> mock_coroutine = mock.Mock()
>>> mock_coroutine.__next__ = mock.Mock()
>>> mock_coroutine.__next__()
<Mock name='mock.__next__()' id='4464139232'>

Suggestion : 2

A mock intended to be used as a property, or other descriptor, on a class. PropertyMock provides __get__() and __set__() methods so you can specify a return value when it is fetched.,The issue is that even if you mock out the call to open() it is the returned object that is used as a context manager (and has __enter__() and __exit__() called).,The patch() decorator / context manager makes it easy to mock classes or objects in a module under test. The object you specify will be replaced with a mock (or other object) during the test and restored when the test ends:,unittest.mock provides a core Mock class removing the need to create a host of stubs throughout your test suite. After performing an action, you can make assertions about which methods / attributes were used and arguments they were called with. You can also specify return values and set needed attributes in the normal way.

>>> from unittest.mock
import MagicMock
   >>>
   thing = ProductionClass() >>>
   thing.method = MagicMock(return_value = 3) >>>
   thing.method(3, 4, 5, key = 'value')
3
   >>>
   thing.method.assert_called_with(3, 4, 5, key = 'value')

>>> mock = Mock(side_effect = KeyError('foo')) >>>
   mock()
Traceback(most recent call last):
   ...
   KeyError: 'foo'

>>> values = {
      'a': 1,
      'b': 2,
      'c': 3
   } >>>
   def side_effect(arg):
   ...
   return values[arg]
      ...
      >>>
      mock.side_effect = side_effect >>>
      mock('a'), mock('b'), mock('c')
      (1, 2, 3) >>>
      mock.side_effect = [5, 4, 3, 2, 1] >>>
      mock(), mock(), mock()
      (5, 4, 3)

>>> from unittest.mock
import patch
   >>>
   @patch('module.ClassName2')
   ...@patch('module.ClassName1')
   ...def test(MockClass1, MockClass2):
   ...module.ClassName1()
   ...module.ClassName2()
   ...assert MockClass1 is module.ClassName1
   ...assert MockClass2 is module.ClassName2
   ...assert MockClass1.called
   ...assert MockClass2.called
   ...
   >>>
   test()

>>> with patch.object(ProductionClass, 'method', return_value = None) as mock_method:
   ...thing = ProductionClass()
   ...thing.method(1, 2, 3)
   ...
   >>>
   mock_method.assert_called_once_with(1, 2, 3)

>>> foo = {
      'key': 'value'
   } >>>
   original = foo.copy() >>>
   with patch.dict(foo, {
      'newkey': 'newvalue'
   }, clear = True):
   ...assert foo == {
      'newkey': 'newvalue'
   }
   ...
   >>>
   assert foo == original

Suggestion : 3

The Python __next__ method returns an arbitrary element that represents the “next” element when you iterate over the object on which it is called. For example, if you iterate over my_object using for x in my_object, Python internally calls my_object.__next__() in each loop iteration to determine the next element. ,__iter__() returns the iterator object — the one that implements the __next__() method. In our case, this is the Data object on which it is called itself. We initialize current_index with zero, so we start iterating with the first index of data.,__next__() returns the next value after one iteration. We increment the current_index attribute to keep track of the current index of the element in data.,Formally, the __next__() method implements the built-in next() function. For example, if you call next(x) an object x, Python internally calls x.__next__() to determine the next element of the iterable object x.

Syntax

object.__next__(self)

Before we learn more about the __next__() dunder method, let’s have a look at a couple of basic next() examples:

users = ['Alice', 'Bob', 'Carl', 'David']

# convert the list to an iterator
users_iterator = iter(users)

x = next(users_iterator)
print(x)
# Output: 'Alice'

x = next(users_iterator)
print(x)
# Output: 'Bob'

x = next(users_iterator)
print(x)
# Output: 'Carl'

x = next(users_iterator)
print(x)
# Output: 'David'

class Data:
   def __init__(self, data):
   self.data = data # an iterable

def __iter__(self):
   self.current_index = 0
return self

def __next__(self):
   if self.current_index < len(self.data):
   x = self.data[self.current_index]
self.current_index += 1
return x
raise StopIteration

The output is as follows: The first four calls result in the expected elements of the data attribute, i.e., 1, 'Alice', 42, and 'finxter'. The fifth call of next() results in a StopIteration error because we have finished iterating over all elements.

1
Alice
42
finxter
Traceback (most recent call last):
File "C:\Users\xcent\Desktop\code.py", line 34, in <module>
   print(next(iterator))
   File "C:\Users\xcent\Desktop\code.py", line 14, in __next__
   raise StopIteration
   StopIteration

Here’s an example:

class Data:
   def __init__(self, data):
   self.data = data # an iterable

d = Data([1, 'Alice', 42, 'finxter'])

# Create an iterator
iterator = iter(d)

Suggestion : 4

Learn how to set up Next.js with commonly used testing tools: Cypress, Playwright, and Jest with React Testing Library.,Stylesheets and images aren't used in the tests but importing them may cause errors, so they will need to be mocked. Create the mock files referenced in the configuration above - fileMock.js and styleMock.js - inside a __mocks__ directory:,If you need to add more setup options before each test, it's common to add them to the jest.setup.js file above.,If your project is using Module Path Aliases, you will need to configure Jest to resolve the imports by matching the paths option in the jsconfig.json file with the moduleNameMapper option in the jest.config.js file. For example:

You can use create-next-app with the with-cypress example to quickly get started.

npx create - next - app @latest--example with - cypress with - cypress - app

To get started with Cypress, install the cypress package:

npm install--save - dev cypress

Add Cypress to the package.json scripts field:

"scripts": {
   "dev": "next dev",
   "build": "next build",
   "start": "next start",
   "cypress": "cypress open",
}

Assuming the following two Next.js pages:

// pages/index.js
import Link from 'next/link'

export default function Home() {
  return (
    <nav>
      <Link href="/about">
        <a>About</a>
      </Link>
    </nav>
  )
}

// pages/about.js
export default function About() {
  return (
    <div>
      <h1>About Page</h1>
    </div>
  )
}