patch

`patch` acts as a function decorator, class decorator or a context
manager. Inside the body of the function or with statement, the `target`
is patched with a `new` object. When the function/with statement exits
the patch is undone.

If `new` is omitted, then the target is replaced with an
`AsyncMock` if the patched object is an async function or a
`MagicMock` otherwise. If `patch` is used as a decorator and `new` is
omitted, the created mock is passed in as an extra argument to the
decorated function. If `patch` is used as a context manager the created
mock is returned by the context manager.

`target` should be a string in the form `'package.module.ClassName'`. The
`target` is imported and the specified object replaced with the `new`
object, so the `target` must be importable from the environment you are
calling `patch` from. The target is imported when the decorated function
is executed, not at decoration time.

The `spec` and `spec_set` keyword arguments are passed to the `MagicMock`
if patch is creating one for you.

In addition you can pass `spec=True` or `spec_set=True`, which causes
patch to pass in the object being mocked as the spec/spec_set object.

`new_callable` allows you to specify a different class, or callable object,
that will be called to create the `new` object. By default `AsyncMock` is
used for async functions and `MagicMock` for the rest.

A more powerful form of `spec` is `autospec`. If you set `autospec=True`
then the mock will be created with a spec from the object being replaced.
All attributes of the mock will also have the spec of the corresponding
attribute of the object being replaced. Methods and functions being
mocked will have their arguments checked and will raise a `TypeError` if
they are called with the wrong signature. For mocks replacing a class,
their return value (the 'instance') will have the same spec as the class.

Instead of `autospec=True` you can pass `autospec=some_object` to use an
arbitrary object as the spec instead of the one being replaced.

By default `patch` will fail to replace attributes that don't exist. If
you pass in `create=True`, and the attribute doesn't exist, patch will
create the attribute for you when the patched function is called, and
delete it again afterwards. This is useful for writing tests against
attributes that your production code creates at runtime. It is off by
default because it can be dangerous. With it switched on you can write
passing tests against APIs that don't actually exist!

Patch can be used as a `TestCase` class decorator. It works by
decorating each test method in the class. This reduces the boilerplate
code when your test methods share a common patchings set. `patch` finds
tests by looking for method names that start with `patch.TEST_PREFIX`.
By default this is `test`, which matches the way `unittest` finds tests.
You can specify an alternative prefix by setting `patch.TEST_PREFIX`.

Patch can be used as a context manager, with the with statement. Here the
patching applies to the indented block after the with statement. If you
use "as" then the patched object will be bound to the name after the
"as"; very useful if `patch` is creating a mock object for you.

Patch will raise a `RuntimeError` if passed some common misspellings of
the arguments autospec and spec_set. Pass the argument `unsafe` with the
value True to disable that check.

`patch` takes arbitrary keyword arguments. These will be passed to
`AsyncMock` if the patched object is asynchronous, to `MagicMock`
otherwise or to `new_callable` if specified.

`patch.dict(...)`, `patch.multiple(...)` and `patch.object(...)` are
available for alternate use-cases.