diff --git a/.flake8 b/.flake8
new file mode 100644
index 0000000..1d1c7f5
--- /dev/null
+++ b/.flake8
@@ -0,0 +1,8 @@
+# vim: ft=cfg
+[flake8]
+max-complexity = 7
+docstring-convention=google
+
+# Required to be compatible with black
+extend-ignore = E203,W503
+inline-quotes = double
diff --git a/.gitignore b/.gitignore
index 4fc828a..0156c35 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,6 @@
 __pycache__/
 .venv/
 backup_tool
+*.egg-info/
+.tox/
+.coverage
diff --git a/.woodpecker.yml b/.woodpecker.yml
new file mode 100644
index 0000000..9673933
--- /dev/null
+++ b/.woodpecker.yml
@@ -0,0 +1,31 @@
+matrix:
+    PYTHON_VERSION:
+        - 3.6
+        - 3.7
+        - 3.8
+        - 3.9
+
+pipeline:
+    test:
+        group: test
+        image: python:${PYTHON_VERSION}-alpine
+        pull: true
+        commands:
+            - pip install -e .[test]
+            - pytest --cov=app --cov-fail-under=90 tests/
+
+    test-pypy:
+        group: test
+        image: pypy:3-7-slim
+        pull: true
+        commands:
+            - pip install -e .[test]
+            - pytest --cov=app --cov-fail-under=90 tests/
+
+    lint:
+        image: python:3.6-alpine
+        commands:
+            - apk update && apk add --no-cache build-base
+            - pip install -e .[lint]
+            - black --check setup.py app
+            - flake8 setup.py app
diff --git a/Makefile b/Makefile
index 5f6e639..ab0f16e 100644
--- a/Makefile
+++ b/Makefile
@@ -1,25 +1,28 @@
 # =====CONFIG=====
-# Devop environment runs in 3.8
-PYTHON=python3.8
+PYTHON := python3.6
+VENV   := .venv
 
 
 # =====RECIPES=====
-.venv/bin/activate: requirements.txt requirements-dev.txt
-	'$(PYTHON)' -m venv .venv
-	.venv/bin/pip install -r requirements.txt -r requirements-dev.txt
+# Create the virtual environment
+$(VENV)/bin/activate: setup.py
+	'$(PYTHON)' -m venv '$(VENV)'
+	'$(VENV)/bin/pip' install -e .[develop]
 
-venv: .venv/bin/activate
+venv: $(VENV)/bin/activate
 .PHONY: venv
 
+# Format the codebase using Black
 format: venv
-	@ .venv/bin/black app/*.py app/**/*.py
+	@ '$(VENV)/bin/black' setup.py app
 .PHONY: format
 
+# Remove any temporary files
 clean:
-	rm -rf .venv
-	rm backup_tool
+	@ rm -rf '$(VENV)' .tox backup_tool
 .PHONY: clean
 
+# Pack the package into a zipfile
 backup_tool:
 	@ cd app && \
 		zip -r ../app.zip * \
@@ -31,5 +34,17 @@ backup_tool:
 app: backup_tool
 .PHONY: app
 
+# Install the app
 install: app
 	cp backup_tool /usr/local/bin
+.PHONY: install
+
+# We can't force the develop to have all the versions locally, so
+# the local tests only include python3.6
+test: venv tox.ini
+	@ '$(VENV)/bin/tox' -e py36
+.PHONY: test
+
+lint: venv
+	@ '$(VENV)/bin/tox' -e lint
+.PHONY: lint
diff --git a/app/__init__.py b/app/__init__.py
new file mode 100644
index 0000000..5927fab
--- /dev/null
+++ b/app/__init__.py
@@ -0,0 +1 @@
+"""Module containing all app code."""
diff --git a/app/__main__.py b/app/__main__.py
index b4cd3a0..1a674ad 100644
--- a/app/__main__.py
+++ b/app/__main__.py
@@ -1,59 +1,65 @@
+"""The main entrypoint of the program."""
 import argparse
 import sys
 from parser import read_specs_file
 
 
-# This just displays the error type and message, not the stack trace
 def except_hook(ext_type, value, traceback):
+    """Make errors not show the stracktrace to stdout.
+
+    Todo:
+        * Replace this with proper error handling
+    """
     sys.stderr.write("{}: {}\n".format(ext_type.__name__, value))
 
 
 # sys.excepthook = except_hook
 
 
-# Define parser
-parser = argparse.ArgumentParser(
-    description="Backup directories and Docker volumes."
-)
-parser.add_argument(
-    "-f",
-    "--file",
-    action="append",
-    dest="file",
-    required=True,
-    help="File containing spec definitions.",
-)
-parser.add_argument(
-    "-j",
-    "--json",
-    action="store_const",
-    const=True,
-    default=False,
-    help="Print out the parsed specs as JSON and exit",
-)
-parser.add_argument(
-    "spec", nargs="*", help="The specs to process. Defaults to all."
-)
+if __name__ == "__main__":
+    # Define parser
+    parser = argparse.ArgumentParser(
+        description="Backup directories and Docker volumes."
+    )
+    parser.add_argument(
+        "-f",
+        "--file",
+        action="append",
+        dest="file",
+        required=True,
+        help="File containing spec definitions.",
+    )
+    parser.add_argument(
+        "-j",
+        "--json",
+        action="store_const",
+        const=True,
+        default=False,
+        help="Print out the parsed specs as JSON and exit",
+    )
+    parser.add_argument(
+        "spec", nargs="*", help="The specs to process. Defaults to all."
+    )
 
-# Parse arguments
-args = parser.parse_args()
-specs = sum([read_specs_file(path) for path in args.file], [])
+    # Parse arguments
+    args = parser.parse_args()
+    specs = sum((read_specs_file(path) for path in args.file), [])
 
-# Filter specs if needed
-if args.spec:
-    specs = list(filter(lambda s: s.name in args.spec, specs))
+    # Filter specs if needed
+    if args.spec:
+        specs = list(filter(lambda s: s.name in args.spec, specs))
 
-# Dump parsed data as json
-if args.json:
-    import json
+    # Dump parsed data as json
+    if args.json:
+        import json
 
-    print(json.dumps([spec.to_dict() for spec in specs], indent=4))
+        # TODO replace this with error handling system
+        print(json.dumps([spec.to_dict() for spec in specs], indent=4))
 
-else:
-    # Run the backups
-    if not specs:
+    elif not specs:
+        # TODO replace this with error handling system
         print("No specs, exiting.")
         sys.exit(0)
 
-    for spec in specs:
-        spec.backup()
+        for spec in specs:
+            spec.backup()
diff --git a/app/exceptions.py b/app/exceptions.py
new file mode 100644
index 0000000..b82bad8
--- /dev/null
+++ b/app/exceptions.py
@@ -0,0 +1,55 @@
+"""Common exceptions raised by the program."""
+from typing import Union, List
+
+
+class InvalidKeyError(Exception):
+    """Thrown when a config file contains an invalid key."""
+
+    def __init__(self, keys: Union[str, List[str]]):
+        """Create a new InvalidKeyError object with the given key.
+
+        Args:
+            keys: the invalid key(s)
+        """
+        if type(keys) == str:
+            keys = [keys]
+
+        self.message = "Invalid key(s): {}".format(", ".join(keys))
+
+        super().__init__()
+
+
+class MissingKeyError(Exception):
+    """Thrown when a required key is missing from a config."""
+
+    def __init__(self, keys: Union[str, List[str]]):
+        """Create a new MissingKeyError object with the given key.
+
+        Args:
+            keys: the invalid key(s)
+        """
+        if type(keys) == str:
+            keys = [keys]
+
+        self.message = "Missing key(s): {}".format(", ".join(keys))
+
+        super().__init__()
+
+
+class InvalidValueError(Exception):
+    """Thrown when a key contains an invalid value."""
+
+    def __init__(self, key: str, expected: str, actual: str):
+        """Create a new InvalidValueError given the arguments.
+
+        Args:
+            key: the key containing the invalid value
+            expected: name of the expected type
+            actual: name of the actual type
+        """
+        self.message = (
+            f"Invalid value for key {key}: expected {expected}, "
+            f"got {actual}"
+        )
+
+        super().__init__()
diff --git a/app/logger.py b/app/logger.py
new file mode 100644
index 0000000..245eeed
--- /dev/null
+++ b/app/logger.py
@@ -0,0 +1,109 @@
+"""This module contains the logging module."""
+from typing import Union
+from pathlib import Path
+from datetime import datetime
+import sys
+
+
+class Logger:
+    """A logger class that logs, ya get the point."""
+
+    LOG_LEVELS = [
+        "debug",
+        "info",
+        "warning",
+        "error",
+        "critical",
+    ]
+    """The log levels' names.
+
+    When used as arguments, the counting starts at 1
+    instead of 0.
+    """
+
+    def __init__(
+        self,
+        log_file: Union[Path, str] = None,
+        append: bool = True,
+        stdout: bool = True,
+        log_level: int = 3,
+    ):
+        """Initialize a new Logger object.
+
+        Args:
+            log_file: path to a log file. If any of the folders within the log
+                file's path don't exist, they will get created. If no value is
+                specified, no log file is created.
+            append: wether or not to append to the existing file or overwrite
+                it. If False, the original file gets deleted during init.
+            stdout: wether or not to log to stdout as well
+            log_level: the minimum level to log
+        """
+        self.log_file = Path(log_file) if log_file else None
+        self.stdout = stdout
+        self.log_level = log_level
+
+        # Remove the original log file
+        if not append:
+            self.log_file.unlink(missing_ok=True)
+
+    def custom(self, message: str, header: str = None):
+        """Log a message given a header and a message.
+
+        If a header is provided (aka truthy), the final form of the messsage
+        wil be:
+
+            `[YYYY-MM-DD HH:MM:SS][header] message`
+
+        Otherwise, it's just:
+
+            `[YYYY-MM-DD HH:MM:SS] message`
+
+        Args:
+            message: the message to display
+            header: the header to add to the message
+        """
+        timestamp = datetime.now().strftime("%Y-%m-%d %H:%M:%S")
+        log_message = f"[{timestamp}] {message}\n"
+
+        if header:
+            log_message = f"[{timestamp}][{header}] {message}\n"
+
+        if self.log_file:
+            self.log_file.write_text(log_message)
+
+        if self.stdout:
+            sys.stdout.write(log_message)
+
+    def log(self, level: int, message: str):
+        """Log a message with a specific level.
+
+        Args:
+            level: log level (index in the LOG_LEVELS variable)
+            message: the message to log
+        """
+        if level < self.log_level:
+            return
+
+        level_name = self.LOG_LEVELS[level - 1].upper()
+        self.custom(level_name, message)
+
+    def debug(self, message: str):
+        """Log a debug message."""
+        self.log(1, message)
+
+    def info(self, message: str):
+        """Log an info message."""
+        self.log(2, message)
+
+    def warning(self, message: str):
+        """Log a warning message."""
+        self.log(3, message)
+
+    def error(self, message: str):
+        """Log an error message."""
+        self.log(4, message)
+
+    def critical(self, message: str):
+        """Log a critical message."""
+        self.log(5, message)
diff --git a/app/notifier.py b/app/notifier.py
index 1848775..903e791 100644
--- a/app/notifier.py
+++ b/app/notifier.py
@@ -1,9 +1,12 @@
+"""Module handling IFTTT notifications."""
 from typing import List
 import os
 import requests
 
 
 class Notifier:
+    """A notifier object that can send IFTTT notifications."""
+
     # (positive, negative)
     _EVENTS = {
         "backup": (
@@ -15,24 +18,40 @@ class Notifier:
             "Couldn't restore {name}.",
         ),
     }
+    """The message content for a given event."""
 
     # Placeholder
     def __init__(
         self, title: str, events: List[str], endpoint: str, api_key: str = None
     ):
+        """Initialize a new Notifier object.
+
+        Args:
+            title: the notification title to use
+            events: the event types that should trigger a notification (should
+                be one of the keys in _EVENTS).
+            endpoint: IFTTT endpoint name
+            api_key: your IFTTT API key. If not provided, it will be read from
+                the IFTTT_API_KEY environment variable.
+
+        Todo:
+            * Read the API key on init
+        """
         self.title = title
         self.events = events
         self.endpoint = endpoint
         self.api_key = api_key
 
     def notify(self, category: str, name: str, status_code: int):
-        """
+        """Send an IFTTT notification.
+
         Args:
-            category: type of notify (e.g. backup or restore)
+            category: type of notify (should be one of the keys in _EVENTS).
+                Only if the category was passed during initialization will the
+                notification be sent.
             name: name of the spec
             status_code: exit code of the command
         """
-
         event = "{}_{}".format(
             category, "success" if status_code == 0 else "failure"
         )
diff --git a/app/parser.py b/app/parser.py
index bbac40c..b02e5a0 100644
--- a/app/parser.py
+++ b/app/parser.py
@@ -1,3 +1,4 @@
+"""Handles parsing a config file from disk."""
 import yaml
 from pathlib import Path
 from typing import List, Union
@@ -6,9 +7,18 @@ import skeleton
 
 
 def read_specs_file(path: Union[str, Path]) -> List[Spec]:
+    """Read a config file and merge it with the skeleton.
+
+    Args:
+        path: path to the yaml config file
+
+    Returns:
+        A list of specs, parsed from the config.
+    """
     with open(path, "r") as yaml_file:
         data = yaml.safe_load(yaml_file)
 
+    # NOTE shouldn't this be defined as a top-level variable?
     categories = [
         ("directories", DirectorySpec),
         ("volumes", VolumeSpec),
@@ -23,6 +33,7 @@ def read_specs_file(path: Union[str, Path]) -> List[Spec]:
 
         # Check what defaults are present
         defaults = {}
+
         if data.get("defaults"):
             if data["defaults"].get("all"):
                 defaults = skeleton.merge(defaults, data["defaults"]["all"])
diff --git a/app/skeleton.py b/app/skeleton.py
index 07c6afb..c12bd45 100644
--- a/app/skeleton.py
+++ b/app/skeleton.py
@@ -1,21 +1,25 @@
+"""Handles merging with the skeleton config."""
 from typing import Dict
-
-
-class InvalidKeyError(Exception):
-    def __init__(self, key):
-        self.message = "Invalid key: {}".format(key)
-
-        super().__init__(key)
-
-
-class MissingKeyError(Exception):
-    def __init__(self, key):
-        self.message = "Missing key: {}".format(key)
-
-        super().__init__(key)
+from .exceptions import InvalidKeyError, MissingKeyError
 
 
 def merge(*dicts: [Dict]) -> Dict:
+    """Merge multiple dicts into one.
+
+    It reads the dicts from left to right, always preferring the "right"
+    dictionary's values. Therefore, the dictionaries should be sorted from
+    least important to most important (e.g. a default values skeleton should be
+    to the left of a dict of selected values).
+
+    Args:
+        dicts: the dictionaries to merge
+
+    Returns:
+        a new dictionary representing the merged dictionaries
+
+    Todo:
+        * Make sure an infinite loop is not possible
+    """
     # Base cases
     if len(dicts) == 0:
         return {}
@@ -44,15 +48,28 @@ def merge(*dicts: [Dict]) -> Dict:
 
 
 def merge_with_skeleton(data: Dict, skel: Dict) -> Dict:
-    """
-    Compare a dict with a given skeleton dict, and fill in default values where
-    needed.
-    """
+    """Merge a dictionary with a skeleton containing default values.
 
+    The skeleton not only defines what the default values are, but also
+    enforces a certain shape. This allows us to define a config file using a
+    dictionary and parse it.
+
+    Args:
+        data: dictionary containing the selected config values
+        skel: dictionary containing the skeleton (aka the def)
+
+    Returns:
+        a new dictionary representing the two merged dictionaries
+
+    Todo:
+        * Check if an infinite loop is possible
+        * Split info less complex functions
+    """
     # First, check for illegal keys
-    for key in data:
-        if key not in skel:
-            raise InvalidKeyError(key)
+    invalid_keys = list(filter(lambda k: k not in skel, data))
+
+    if invalid_keys:
+        raise InvalidKeyError(invalid_keys)
 
     # Then, check the default values
     for key, value in skel.items():
@@ -66,6 +83,7 @@ def merge_with_skeleton(data: Dict, skel: Dict) -> Dict:
 
         # Error if value is not same type as default value
         elif type(data[key]) != type(value) and value is not None:
+            # TODO make this error message more verbose
             raise TypeError("Invalid value type")
 
         # Recurse into dicts
diff --git a/app/specs/__init__.py b/app/specs/__init__.py
index 0192b9e..dd08c1c 100644
--- a/app/specs/__init__.py
+++ b/app/specs/__init__.py
@@ -1,4 +1,7 @@
+"""Parent module for the various spec types."""
 from .spec import Spec
 from .directory import DirectorySpec
 from .volume import VolumeSpec
 from .container import ContainerSpec
+
+__all__ = ["Spec", "DirectorySpec", "VolumeSpec", "ContainerSpec"]
diff --git a/app/specs/container.py b/app/specs/container.py
index bef6f8c..79d4d3a 100644
--- a/app/specs/container.py
+++ b/app/specs/container.py
@@ -1,3 +1,4 @@
+"""Module defining a container-based spec."""
 from .spec import Spec
 from typing import Union
 from pathlib import Path
@@ -6,11 +7,10 @@ import subprocess
 
 
 class ContainerSpec(Spec):
-    """
-    A spec for backing up via a container.
-    """
+    """Spec for backing up via a container."""
 
     _SKEL = {"container": None, "command": None, "mountpoint": "/from"}
+    """The skeleton for the ContainerSpec config."""
 
     def __init__(
         self,
@@ -23,6 +23,21 @@ class ContainerSpec(Spec):
         mountpoint: str,
         notify=None,
     ):
+        """Create a new ContainerSpec object.
+
+        Args:
+            name: name of the spec (used as an identifier)
+            container: the Docker container to back up
+            destination: where to store the backups (gets created if
+                non-existent)
+            limit: max amount of backups to keep
+            command: command to run inside the container. This command should
+                perform a specified backup and output this data to stdout. This
+                output then gets piped to a backup file.
+            extension: the extension of the backup files.
+            mountpoint: I don't actually know, this never gets used
+            notify: notifier object (may be None)
+        """
         super().__init__(name, destination, limit, extension, notify)
 
         self.container = container
@@ -30,6 +45,7 @@ class ContainerSpec(Spec):
         self.command = command
 
     def backup(self):
+        """Create a new backup."""
         # Remove excess backups
         self.remove_backups()
 
diff --git a/app/specs/directory.py b/app/specs/directory.py
index 9747b5b..b8fbc32 100644
--- a/app/specs/directory.py
+++ b/app/specs/directory.py
@@ -1,3 +1,4 @@
+"""Module defining a directory-based spec."""
 from .spec import Spec
 from pathlib import Path
 from typing import Union
@@ -6,9 +7,7 @@ from datetime import datetime
 
 
 class DirectorySpec(Spec):
-    """
-    A spec for backing up a local directory.
-    """
+    """A spec for backing up a local directory."""
 
     _SKEL = {
         "source": None,
@@ -25,6 +24,17 @@ class DirectorySpec(Spec):
         extension: str,
         notify=None,
     ):
+        """Initialize a new DirectorySpec object.
+
+        Args:
+            name: name of the spec
+            source: what directory to back up
+            destination: where to store the backup
+            limit: how many backups to keep
+            command: what command to use to create the backup
+            extension: extension of the backup files
+            notify: a Notifier object that handles sending notifications
+        """
         super().__init__(name, destination, limit, extension, notify)
 
         self.source = source if type(source) == Path else Path(source)
@@ -38,6 +48,7 @@ class DirectorySpec(Spec):
         self.command = command
 
     def backup(self):
+        """Create a new backup."""
         # Remove excess backups
         self.remove_backups()
 
diff --git a/app/specs/spec.py b/app/specs/spec.py
index 9b372ef..f26f54b 100644
--- a/app/specs/spec.py
+++ b/app/specs/spec.py
@@ -1,4 +1,4 @@
-from pathlib import Path
+"""This module contains the base Spec class."""
 from typing import Union, Dict
 import skeleton
 import os
@@ -7,9 +7,7 @@ import inspect
 
 
 class Spec:
-    """
-    Base class for all other spec types.
-    """
+    """Base class for all other spec types."""
 
     _SKEL = {
         "destination": None,
@@ -31,23 +29,26 @@ class Spec:
         extension: str,
         notify=None,
     ):
-        """
+        """Initialize a new Spec object.
+
+        This initializer usually gets called by a subclass's init instead of
+        directly.
+
         Args:
             name: name of the spec
             destination: directory where the backups shall reside
             limit: max amount of backups
-            notifier: notifier object
+            extension: file extension of the backup files
+            notify: notifier object to send IFTT notifications
         """
-
         self.name = name
-        self.destination = (
-            destination if type(destination) == Path else Path(destination)
-        )
+        self.destination = Path(destination)
 
         # Create destination if non-existent
         try:
             self.destination.mkdir(parents=True, exist_ok=True)
 
+        # TODO just make this some checks in advance
         except FileExistsError:
             raise NotADirectoryError(
                 "{} already exists, but isn't a directory.".format(
@@ -60,16 +61,24 @@ class Spec:
         self.extension = extension
 
     @classmethod
-    def skeleton(cls):
+    def skeleton(cls: "Spec") -> Dict:
+        """Return the skeleton for the given class.
+
+        It works by inspecting the inheritance tree and merging the skeleton
+        for each of the parents.
+
+        Args:
+            cls: the class to get the skeleton for
+
+        Returns:
+            a dictionary containing the skeleton
+        """
         return skeleton.merge(
             *[val._SKEL for val in reversed(inspect.getmro(cls)[:-1])]
         )
 
     def remove_backups(self):
-        """
-        Remove all backups exceeding the limit
-        """
-
+        """Remove all backups exceeding the limit."""
         files = sorted(
             self.destination.glob("*." + self.extension),
             key=os.path.getmtime,
@@ -81,13 +90,22 @@ class Spec:
                 path.unlink()
 
     def backup(self):
+        """Create a new backup.
+
+        This function should be implemented by the subclasses.
+        """
         raise NotImplementedError()
 
     def restore(self):
+        """Restore a given backup (NOT IMPLEMENTED).
+
+        This function should be implemented by the subclasses.
+        """
         raise NotImplementedError()
 
     @classmethod
     def from_dict(cls, name, obj: Dict, defaults: Dict) -> "Spec":
+        """Create the class given a dictionary (e.g. from a config)."""
         # Combine defaults with skeleton, creating new skeleton
         skel = skeleton.merge(cls.skeleton(), defaults)
 
@@ -97,4 +115,8 @@ class Spec:
         return cls(name, **obj)
 
     def to_dict(self):
+        """Export the class as a dictionary.
+
+        This function should be imnplemented by the subclasses.
+        """
         raise NotImplementedError()
diff --git a/app/specs/volume.py b/app/specs/volume.py
index cd9d937..403c51b 100644
--- a/app/specs/volume.py
+++ b/app/specs/volume.py
@@ -1,3 +1,4 @@
+"""Module defining a Docker volume-based spec."""
 from .spec import Spec
 from typing import Union
 from pathlib import Path
@@ -6,9 +7,7 @@ import subprocess
 
 
 class VolumeSpec(Spec):
-    """
-    A spec for backing up a Docker volume.
-    """
+    """A spec for backing up a Docker volume."""
 
     _SKEL = {
         "volume": None,
@@ -27,6 +26,18 @@ class VolumeSpec(Spec):
         extension: str,
         notify=None,
     ):
+        """Initialize a new VolumeSpec object.
+
+        Args:
+            name: name of the spec
+            volume: Docker volume to back up
+            image: base image to use to run backup command
+            destination: where to store the backup files
+            limit: max backup files to keep
+            command: backup command to run within the base image
+            extension: file extension of the backup files
+            notify: Notifier object
+        """
         super().__init__(name, destination, limit, extension, notify)
 
         self.volume = volume
@@ -34,6 +45,7 @@ class VolumeSpec(Spec):
         self.command = command
 
     def backup(self):
+        """Create a new backup."""
         # Remove excess backups
         self.remove_backups()
 
@@ -42,8 +54,10 @@ class VolumeSpec(Spec):
             datetime.now().strftime("%Y-%m-%d_%H-%M-%S"), self.extension
         )
 
+        base_cmd = "docker run --rm -v '{}:/from' -v '{}:/to' -w /from '{}' {}"
+
         process = subprocess.run(
-            "docker run --rm -v '{}:/from' -v '{}:/to' -w /from '{}' {}".format(
+            base_cmd.format(
                 self.volume,
                 self.destination,
                 self.image,
diff --git a/renovate.json b/renovate.json
new file mode 100644
index 0000000..9775346
--- /dev/null
+++ b/renovate.json
@@ -0,0 +1,3 @@
+{
+    "$schema": "https://docs.renovatebot.com/renovate-schema.json"
+}
diff --git a/requirements-dev.txt b/requirements-dev.txt
deleted file mode 100644
index 3eed54f..0000000
--- a/requirements-dev.txt
+++ /dev/null
@@ -1,10 +0,0 @@
-# Language server
-jedi==0.18.0
-
-# Linting & Formatting
-black==20.8b1
-flake8==3.8.4
-
-# Testing
-tox==3.21.1
-pytest==6.2.1
diff --git a/setup.cfg b/setup.cfg
new file mode 100644
index 0000000..568b586
--- /dev/null
+++ b/setup.cfg
@@ -0,0 +1,25 @@
+[options.extras_require]
+# Used to run the tests inside the CICD pipeline
+ci =
+    tox==3.23.1
+
+# Used inside Tox for running tests
+test =
+    pytest==6.2.4
+    pytest-cov==2.12.1
+
+# Used inside tox for linting
+lint =
+    black==20.8b1
+    flake8==3.9.2
+    flake8-bugbear==21.4.3
+    flake8-comprehensions==3.5.0
+    flake8-docstrings==1.6.0
+    flake8-print==4.0.0
+    flake8-quotes==3.2.0
+
+# Required for the developer
+develop =
+    %(ci)s
+    %(lint)s
+    jedi==0.18.0
diff --git a/setup.py b/setup.py
new file mode 100644
index 0000000..0b00eae
--- /dev/null
+++ b/setup.py
@@ -0,0 +1,10 @@
+from setuptools import setup
+
+setup(
+    name="backup-tool",
+    version="0.1.0",
+    author="Jef Roosens",
+    description="A utility to simply backing up services.",
+    # TODO add license
+    packages=["app", "tests"],
+)
diff --git a/requirements.txt b/tests/__init__.py
similarity index 100%
rename from requirements.txt
rename to tests/__init__.py
diff --git a/tests/test_dict_merge.py b/tests/test_dict_merge.py
new file mode 100644
index 0000000..2da81bf
--- /dev/null
+++ b/tests/test_dict_merge.py
@@ -0,0 +1,69 @@
+"""Tests for the skeleton module."""
+from app.skeleton import merge
+
+
+def test_merge_empty():
+    """Test correct response for an empty merge."""
+    assert merge() == {}
+
+
+def test_merge_single():
+    """Test merge command with a single input."""
+    assert merge({}) == {}
+
+    dic = {"test": "value", "test2": "value2"}
+
+    assert merge(dic) == dic
+
+
+def test_merge_double_no_overlap():
+    """Test merge command with two non-overlapping inputs."""
+    d1 = {"test": "value", "test2": "value2"}
+    d2 = {"test3": "value3"}
+    d_res = {"test": "value", "test2": "value2", "test3": "value3"}
+
+    assert merge(d1, d2) == d_res
+
+
+def test_merge_double_overlap():
+    """Test merge command with two overlapping inputs."""
+    d1 = {"test": "value", "test2": "value2"}
+    d2 = {"test2": "value3"}
+    d_res = {"test": "value", "test2": "value3"}
+
+    assert merge(d1, d2) == d_res
+
+
+def test_merge_triple_no_overlap():
+    """Test merge command with three non-overlapping inputs.
+
+    This test tells us that the recursion works.
+    """
+    d1 = {"test": "value", "test2": "value2"}
+    d2 = {"test3": "value3"}
+    d3 = {"test4": "value4"}
+    d_res = {
+        "test": "value",
+        "test2": "value2",
+        "test3": "value3",
+        "test4": "value4",
+    }
+
+    assert merge(d1, d2, d3) == d_res
+
+
+def test_merge_triple_overlap():
+    """Test merge command with three overlapping inputs.
+
+    This test tells us that the recursion works.
+    """
+    d1 = {"test": "value", "test2": "value2"}
+    d2 = {"test3": "value3"}
+    d3 = {"test2": "value4"}
+    d_res = {
+        "test": "value",
+        "test2": "value4",
+        "test3": "value3",
+    }
+
+    assert merge(d1, d2, d3) == d_res
diff --git a/tests/test_logger.py b/tests/test_logger.py
new file mode 100644
index 0000000..ff2debd
--- /dev/null
+++ b/tests/test_logger.py
@@ -0,0 +1,23 @@
+"""Tests for the logger module."""
+from app.logger import Logger
+from datetime import datetime
+
+
+def test_custom_stdout(capfd):
+    """Test the custom command."""
+    logger = Logger()
+
+    timestamp = datetime.now().strftime("%Y-%m-%d %H:%M:%S")
+    logger.custom("a message", header="cewl")
+
+    out, _ = capfd.readouterr()
+
+    assert out == f"[{timestamp}][cewl] a message\n"
+
+
+def test_log_stdout(capfd):
+    """Test the log command with several levels."""
+
+    logger = Logger()
+
+    # TODO
diff --git a/tests/test_skeleton.py b/tests/test_skeleton.py
new file mode 100644
index 0000000..9ade87e
--- /dev/null
+++ b/tests/test_skeleton.py
@@ -0,0 +1,70 @@
+"""Tests wether the skeleton merge works."""
+from app.skeleton import merge_with_skeleton
+from app.exceptions import InvalidKeyError, MissingKeyError
+import pytest
+
+
+def test_single_invalid_key():
+    """Tests wether an InvalidKeyError is correctly thrown for a single key."""
+    data = {
+        "test": 1,
+        "test2": "test"
+    }
+    skel = {
+        "test": None,
+    }
+
+    with pytest.raises(InvalidKeyError) as e_info:
+        merge_with_skeleton(data, skel)
+
+    assert e_info.value.message == "Invalid key(s): test2"
+
+
+def test_multiple_invalid_keys():
+    """Tests wether an InvalidKeyError is thrown for multiple keys."""
+    data = {
+        "test": 1,
+        "test2": "test",
+        "test3": "test",
+    }
+    skel = {
+        "test": None,
+    }
+
+    with pytest.raises(InvalidKeyError) as e_info:
+        merge_with_skeleton(data, skel)
+
+    assert e_info.value.message == "Invalid key(s): test2, test3"
+
+
+def test_single_missing_key():
+    """Tests wether a MissingKeyError is correctly thrown for a single key."""
+    data = {
+        "test": 1,
+    }
+    skel = {
+        "test": None,
+        "test2": None,
+    }
+
+    with pytest.raises(MissingKeyError) as e_info:
+        merge_with_skeleton(data, skel)
+
+    assert e_info.value.message == "Missing key(s): test2"
+
+
+def test_multiple_missing_keys():
+    """Tests wether a MissingKeyError is correctly thrown for multiple keys."""
+    data = {
+        "test": 1,
+    }
+    skel = {
+        "test": None,
+        "test2": None,
+        "test3": None,
+    }
+
+    with pytest.raises(MissingKeyError) as e_info:
+        merge_with_skeleton(data, skel)
+
+    assert e_info.value.message == "Missing key(s): test2, test3"
diff --git a/tox.ini b/tox.ini
new file mode 100644
index 0000000..847ba45
--- /dev/null
+++ b/tox.ini
@@ -0,0 +1,15 @@
+[tox]
+envlist = py36,py37,pypy37,py38,py39,lint
+
+[testenv]
+deps = .[test]
+commands =
+    pytest
+    pytest --cov=app --cov-fail-under=90 tests/
+
+[testenv:lint]
+basepython = python3.6
+deps = .[lint]
+commands =
+    black --check setup.py app
+    flake8 setup.py app