kgb
Utilities for spying on function calls in unit tests.
Decision gist · record as of 2026-08-14
Yes. kgb is a lightweight, actively maintained testing utility with no dependencies, permissive licensing, and a clean API for function call verification. It's well-suited for any Python test suite that needs spy functionality without the overhead of full mocking frameworks.AI-flagged interpretation of the facts on this page — verify before relying
Before you install
- Low friction: pure Python wheel with no runtime dependencies.
- Actively maintained with a recent release and active repository.
License · maintenance · safety
MIT (permissive) — MIT license is permissive; you can use kgb in commercial and proprietary projects with minimal restrictions.
last release 2025-12-11 (246 days) · last repo commit 2026-07-07 · 53 stars
0 known vulnerabilities (OSV.dev, 2026-08-14) · 9,403,872 downloads/mo, #1,536 on PyPI
Alternatives
Verify before relying
pip install kgb
from kgb import SpyAgency
agency = SpyAgency()
agency.spy_on(obj.function)
obj.function()
print(obj.function.called) # True
print(obj.function.last_call.args)- Whether kgb works with Python 2.7 as documented (support statement says 2.7 and 3.6–3.11, but classifiers list 3.12–3.13)
What it is and what it does
kgb is a spy library for Python unit tests that intercepts function calls without requiring you to write mock objects. When you spy on a function, kgb records every call—its arguments, return value, and any exceptions—and lets you query that history in your test assertions. You can configure a spy to call the original function, block it entirely, or reroute it to a fake function you provide.
The library integrates with unittest, pytest, nose, and nose2, and can be used as a mixin in test classes, a context manager for quick one-off spies, or through a SpyAgency object that manages multiple spies. It has no runtime dependencies and installs as a pure Python wheel, making it lightweight and easy to add to any test suite.
Use it for
- Verify that a method was called with specific arguments without mocking the entire object
- Count how many times a function is invoked during a test to ensure it's not called more than expected
- Block a function call in tests (e.g., prevent side effects) while still recording that it was attempted
- Reroute a function to a fake implementation to test error handling or alternative behavior
- Track the sequence and details of multiple function calls across a test to verify interaction order
Worth the install?
AI-flagged interpretation of the facts on this page. Verify before relying on it.
Yes.
kgb is a lightweight, actively maintained testing utility with no dependencies, permissive licensing, and a clean API for function call verification. It's well-suited for any Python test suite that needs spy functionality without the overhead of full mocking frameworks.
Install
kgb on PyPI
Before you install
Low friction: pure Python wheel with no runtime dependencies. Actively maintained with a recent release and active repository.
License in practice
MIT license is permissive; you can use kgb in commercial and proprietary projects with minimal restrictions.
Quickstart
pip install kgb
from kgb import SpyAgency
agency = SpyAgency()
agency.spy_on(obj.function)
obj.function()
print(obj.function.called) # True
print(obj.function.last_call.args)Verify before relying
- Whether kgb works with Python 2.7 as documented (support statement says 2.7 and 3.6–3.11, but classifiers list 3.12–3.13)
Package facts
| License | MIT permissive |
| Python support | Supports the current Python release !=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*,!=3.5.*,>=2.7 |
| Install friction | Low. Pure-Python wheel |
| Runtime dependencies | None |
| Maintenance | Actively maintained 246 days since the last release |
| Last repo commit | |
| First released | |
| Downloads | 9,403,872 / month, #1,536 on PyPI 30-day window, as of 2026-08-14 |
| Known vulnerabilities | None known OSV.dev, checked 2026-08-14 |
| Classifiers | Development Status :: 5 - Production/StableEnvironment :: Other EnvironmentFramework :: PytestIntended Audience :: DevelopersLicense :: OSI Approved :: MIT LicenseOperating System :: OS IndependentProgramming Language :: PythonProgramming Language :: Python :: 2Programming Language :: Python :: 2.7Programming Language :: Python :: 3Programming Language :: Python :: 3.10Programming Language :: Python :: 3.11Programming Language :: Python :: 3.12Programming Language :: Python :: 3.13Programming Language :: Python :: 3.6Programming Language :: Python :: 3.7Programming Language :: Python :: 3.8Programming Language :: Python :: 3.9Topic :: Software DevelopmentTopic :: Software Development :: Libraries :: Python ModulesTopic :: Software Development :: Testing |
Evidence: kgb-7.3-py2.py3-none-any.whl
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See also pytest-mock · snoop · pytest-logger · seeq-spy · flexmock · pyfakefs · pytest-subtests · pytest-faker · wrapt · nose2