Skip to main content

Type safe mocking

Project description

typemock

Build Status Documentation Status Pyversions

Type safe mocking for python 3.

  1. Motivation
  2. Installation
  3. Quick example usage

NOTE: This library is still in Alpha. Its API and implementation could change.

Detailed Documentation

Motivation

The mocking tools in python are powerful, flexible and useful for building independent tests at various levels.

This flexibility is part of what is considered a strength of the python language, and possibly any dynamically typed language.

However, this flexibility comes at a cost.

It is possible to build mocks which do not conform to the actual behaviour or contract defined by the things they are mocking. Or, for them to be initially correct, and then to go out of sync with actual behaviour and for tests to remain green.

We do not have compile time protections for us doing things with/to things which do not align with the contracts they define and the clients of those contracts expect.

But, now we have type hints. And so, we can explicitly define the contracts of our objects, and, if we have done this, we can mock them in a type safe way as well. This is what this library aims to help achieve. Type safe mocking.

Used in conjunction with mypy, this should result in much more high fidelity independent tests.

Installation

pip install typemock

Quick Example Usage

Given some class (the implementation of its method is not relevant)

class MyThing:

    def multiple_arg(self, prefix: str, number: int) -> str:
        pass

Mock and verify

We con mock behaviour and verify interactions as follows:

from typemock import tmock, when, verify

expected_result = "a string"

with tmock(MyThing) as my_thing_mock:
    when(my_thing_mock.multiple_arg("p", 1)).then_return(expected_result)

actual = my_thing_mock.multiple_arg(
    number=1,
    prefix="p"
)

assert expected_result == actual
verify(my_thing_mock).multiple_arg("p", 1)

Type safety

And when we try to specify behaviour that does not conform to the contract of the object we are mocking

expected_result = "a string"

with tmock(MyThing) as my_thing_mock:
    when(my_thing_mock.multiple_arg(prefix="p", number="should be an int")).then_return(expected_result)

We get an informative error such as

typemock.safety.MockTypeSafetyError: Method: multiple_arg Arg: number must be of type:<class 'int'>

Project details


Download files

Download the file for your platform. If you're not sure which to choose, learn more about installing packages.

Files for typemock, version 0.5.1
Filename, size File type Python version Upload date Hashes
Filename, size typemock-0.5.1-py3-none-any.whl (23.6 kB) File type Wheel Python version py3 Upload date Hashes View hashes
Filename, size typemock-0.5.1.tar.gz (16.9 kB) File type Source Python version None Upload date Hashes View hashes

Supported by

Elastic Elastic Search Pingdom Pingdom Monitoring Google Google BigQuery Sentry Sentry Error logging AWS AWS Cloud computing DataDog DataDog Monitoring Fastly Fastly CDN SignalFx SignalFx Supporter DigiCert DigiCert EV certificate StatusPage StatusPage Status page