test: unit tests for config, filters, client and inventory building

pytest suite with mocked NetBox API responses, plus a makefile driving
venv setup, tests, linting and formatting.

makefile

@@ -0,0 +1,35 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+# Copyright (C) 2026 Bryan Joshua Pedini
+.PHONY: help dev-environment test lint lint-fix format clean
+
+VENV ?= .venv
+PYTHON ?= $(VENV)/bin/python
+
+help:
+	@echo "Available targets:"
+	@echo "  dev-environment  create the virtualenv and install dev dependencies"
+	@echo "  test             run the unit test suite"
+	@echo "  lint             run ruff checks"
+	@echo "  lint-fix         run ruff checks and fix what is auto-fixable"
+	@echo "  format           run the ruff formatter"
+	@echo "  clean            remove the virtualenv and caches"
+
+dev-environment:
+	python3 -m venv $(VENV)
+	$(PYTHON) -m pip install --upgrade pip
+	$(PYTHON) -m pip install requests PyYAML pytest responses ruff
+
+test:
+	$(PYTHON) -m pytest
+
+lint:
+	$(PYTHON) -m ruff check .
+
+lint-fix:
+	$(PYTHON) -m ruff check --fix .
+
+format:
+	$(PYTHON) -m ruff format .
+
+clean:
+	rm -rf $(VENV) .pytest_cache .ruff_cache __pycache__ tests/__pycache__