diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
new file mode 100644
index 0000000..ab147ec
--- /dev/null
+++ b/.github/workflows/tests.yml
@@ -0,0 +1,67 @@
+name: Tests
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+
+  tests:
+    runs-on: ${{ matrix.os }}
+
+    strategy:
+      matrix:
+        os: [ "ubuntu-latest", "macos-latest" ]
+        python-version: [ "3.6", "3.7", "3.8", "3.9", "3.10" ]
+      fail-fast: false
+
+    env:
+      OS: ${{ matrix.os }}
+      PYTHON: ${{ matrix.python-version }}
+
+    defaults:
+      run:
+        shell: bash
+
+    name: Python ${{ matrix.python-version }} on ${{ matrix.os }}
+    steps:
+
+      - name: Acquire sources
+        uses: actions/checkout@v3
+
+      - name: Setup Python
+        uses: actions/setup-python@v4
+        with:
+          python-version: ${{ matrix.python-version }}
+          architecture: x64
+          cache: 'pip'
+          cache-dependency-path: 'setup.py'
+
+      - name: Install prerequisites (Linux)
+        if: matrix.os == 'ubuntu-latest'
+        run: |
+          sudo apt install --yes libsnmp-dev snmp-mibs-downloader
+
+      - name: Install prerequisites (macOS)
+        if: matrix.os == 'macos-latest'
+        run: |
+          brew install net-snmp
+
+      - name: Run linter
+        run: |
+          make lint
+
+      - name: Run tests, with coverage
+        run: |
+          make test
+
+      - name: Upload coverage results to Codecov
+        uses: codecov/codecov-action@v3
+        with:
+          file: ./coverage.xml
+          flags: unittests
+          env_vars: OS,PYTHON
+          name: codecov-umbrella
+          fail_ci_if_error: false
diff --git a/.gitignore b/.gitignore
index 8468f27..d4d043a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,3 +2,5 @@
 .venv*
 __pycache__
 *.egg-info
+.coverage
+coverage.xml
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..f6bb000
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,34 @@
+$(eval venv         := .venv)
+$(eval pip          := $(venv)/bin/pip)
+$(eval python       := $(venv)/bin/python)
+$(eval black        := $(venv)/bin/black)
+$(eval isort        := $(venv)/bin/isort)
+$(eval pytest       := $(venv)/bin/pytest)
+$(eval twine        := $(venv)/bin/twine)
+$(eval flake8       := $(venv)/bin/pflake8)
+$(eval proselint    := $(venv)/bin/proselint)
+
+setup-virtualenv:
+	@test -e $(python) || python3 -m venv $(venv) || python -m venv $(venv)
+
+format: setup-virtualenv
+	$(pip) install --requirement=requirements-utils.txt
+	$(black) .
+	$(isort) .
+
+lint: setup-virtualenv
+	$(pip) install --requirement=requirements-utils.txt
+	$(flake8) --exit-zero *.py
+	$(MAKE) proselint
+
+proselint:
+	$(proselint) *.md || true
+
+test: setup-virtualenv
+	$(pip) install --editable=.[test]
+	$(pytest)
+
+publish: setup-virtualenv
+	$(pip) install build twine
+	$(python) -m build
+	$(twine) upload --skip-existing --verbose dist/*{.tar.gz,.whl}
diff --git a/README.md b/README.md
index 719f74c..fed9e28 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,8 @@
-# check_synology [![Release](https://img.shields.io/github/release/wernerfred/check_synology.svg)](https://github.com/wernerfred/check_synology/releases)
+# check_synology
+
+[![Tests](https://github.com/wernerfred/check_synology/actions/workflows/tests.yml/badge.svg)](https://github.com/wernerfred/check_synology/actions/workflows/tests.yml)
+[![Code coverage](https://codecov.io/gh/wernerfred/check_synology/branch/master/graph/badge.svg)](https://codecov.io/gh/wernerfred/check_synology)
+[![Release](https://img.shields.io/github/release/wernerfred/check_synology.svg)](https://github.com/wernerfred/check_synology/releases)
 
 
 ## About
@@ -81,20 +85,18 @@ ln -s $(which check_synology) /usr/lib/nagios/plugins/check_synology
 
 ## Development
 
-For setting up a development sandbox, you might want to follow this walkthrough.
+For setting up a development sandbox and running the software tests, you might
+want to follow this walkthrough.
 
-Acquire sources:
 ```shell
 git clone https://github.com/wernerfred/check_synology
 cd check_synology
+make test
 ```
 
-Install program in development mode into a Python virtual environment:
-```shell
-python3 -m venv .venv
-source .venv/bin/activate
-pip install --editable=.
-```
+By running `make test`, a Python virtual environment will be created within the
+`.venv` folder of your working tree. Use `source .venv/bin/activate` to
+activate it.
 
 ## Contributors ✨
 
diff --git a/pyproject.toml b/pyproject.toml
new file mode 100644
index 0000000..5d74761
--- /dev/null
+++ b/pyproject.toml
@@ -0,0 +1,28 @@
+[tool.black]
+line-length = 120
+
+[tool.isort]
+profile = "black"
+line_length = 120
+multi_line_output = 3
+
+[tool.flake8]
+max-line-length = 120
+
+[tool.pytest.ini_options]
+minversion = "2.0"
+addopts = "-rsfEX -p pytester --strict-markers --verbosity=3 --cov --cov-report=term-missing --cov-report=xml"
+log_level = "DEBUG"
+testpaths = ["testing"]
+xfail_strict = true
+markers = [
+]
+
+[tool.coverage.run]
+omit = [
+    "testing/*",
+]
+
+[tool.coverage.report]
+fail_under = 0
+show_missing = true
diff --git a/requirements-utils.txt b/requirements-utils.txt
new file mode 100644
index 0000000..15f02a6
--- /dev/null
+++ b/requirements-utils.txt
@@ -0,0 +1,5 @@
+black
+isort
+pyproject-flake8
+flake8<5
+proselint
diff --git a/setup.py b/setup.py
index abc930f..6e97c3f 100644
--- a/setup.py
+++ b/setup.py
@@ -21,20 +21,33 @@ def read(path):
     long_description=long_description,
     long_description_content_type="text/markdown",
     platforms=["any"],
-    license="AGPL-3.0",
+    license="MIT",
     keywords="synology, synology-diskstation, snmp, snmpv3, monitoring, monitoring-plugin, nagios, icinga2, icinga2-plugin",
     py_modules=["check_synology"],
-    entry_points={"console_scripts": ["check_synology = check_synology"]},
-    python_requires=">=3.4",
+    entry_points={"console_scripts": ["check_synology = check_synology:__main__"]},
+    python_requires=">=3.6",
     install_requires=["easysnmp>=0.2.6,<1"],
+    extras_require={
+        "test": [
+            "pytest<8",
+            "pytest-mock<4",
+            "pytest-cov<4",
+        ],
+    },
     classifiers=[
         "Development Status :: 4 - Beta",
-        "License :: OSI Approved :: GNU Affero General Public License v3",
+        "License :: OSI Approved :: MIT License",
         "Natural Language :: English",
         "Operating System :: OS Independent",
         "Environment :: Console",
         "Programming Language :: Python",
+        "Programming Language :: Python",
         "Programming Language :: Python :: 3",
+        "Programming Language :: Python :: 3.6",
+        "Programming Language :: Python :: 3.7",
+        "Programming Language :: Python :: 3.8",
+        "Programming Language :: Python :: 3.9",
+        "Programming Language :: Python :: 3.10",
         "Programming Language :: Python :: Implementation :: CPython",
         "Intended Audience :: Developers",
         "Intended Audience :: Education",
diff --git a/testing/test_cli.py b/testing/test_cli.py
new file mode 100644
index 0000000..8055d34
--- /dev/null
+++ b/testing/test_cli.py
@@ -0,0 +1,40 @@
+import sys
+
+
+def run_program(*args) -> int:
+    """
+    Run `check_synology` program and return exit code.
+
+    Support a variable number of command line options.
+    """
+    sys.argv = ["check_synology", *args]
+    try:
+        import check_synology
+    except SystemExit as ex:
+        return ex.code % 256
+
+
+def test_no_options(capsys):
+    """
+    Verify running the program without options croaks as expected.
+    """
+    exitcode = run_program()
+    response = capsys.readouterr()
+    assert exitcode == 2
+    assert response.out == ""
+    assert (
+        "check_synology: error: the following arguments are required: "
+        "hostname, username, authkey, privkey, mode" in response.err
+    )
+
+
+def test_help(capsys):
+    """
+    Verify running the program with the `--help` option works as expected.
+    """
+    exitcode = run_program("--help")
+    response = capsys.readouterr()
+    assert exitcode == 0
+    assert "the hostname" in response.out
+    assert "critical value for selected mode" in response.out
+    assert response.err == ""