diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..287f16a
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,6 @@
+__pycache__
+/.coverage
+/dist/
+/htmlcov/
+/*.egg-info/
+ionit.1
diff --git a/LICENSE b/LICENSE
new file mode 100755
index 0000000..f92acda
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,15 @@
+ionit is licensed under ISC:
+
+Copyright (C) 2018, Benjamin Drung <benjamin.drung@profitbricks.com>
+
+Permission to use, copy, modify, and/or distribute this software for any
+purpose with or without fee is hereby granted, provided that the above
+copyright notice and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
diff --git a/MANIFEST.in b/MANIFEST.in
new file mode 100644
index 0000000..cdf4e2d
--- /dev/null
+++ b/MANIFEST.in
@@ -0,0 +1,4 @@
+recursive-include tests *.jinja *.json *.py *.yaml echo pylint.conf
+include ionit.1.md
+include ionit.py
+include LICENSE
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..0af9629
--- /dev/null
+++ b/README.md
@@ -0,0 +1,131 @@
+ionit
+=====
+
+ionit is a simple and small configuration templating tool. It collects a context
+and renders Jinja templates in a given directory. The context can be either
+static JSON or YAML files or dynamic Python files. Python files can also define
+functions passed through to the rendering.
+
+The context filenames needs to end with `.json` for JSON, `.py` for Python,
+and `.yaml` for YAML. The context files are read in alphabetical order. If the
+same key is defined by multiple context files, the file that is read later takes
+precedence. It is recommended to prefix the files with a number in case the
+order is relevant.
+
+ionit comes with an early boot one shot service that is executed before the
+networking service which allows one to generate configurations files for the
+networking and other services before they are started. In this regard, ionit can
+act as tiny stepbrother of cloud-init.
+
+Python modules
+==============
+
+Python modules can define a `collect_context` function. This function is called
+by ionit and the current context is passed as parameter. The current context can
+be used to derive more context information, but this variable should not be
+modified. `collect_context` must return a dictionary (can be empty) or raise an
+exception, which will be caught by ionit.
+
+Python modules can also define functions which can be called from the Jinja
+template on rendering. Use the `ionit_plugin.function` decorator to mark the
+functions to export.
+
+Note that the functions names should not collide with other keys from the
+context. If one Python module defines a function and a value in the context
+with the same name, the value in the context will take precedence.
+
+An example Python module might look like:
+
+```python
+import ionit_plugin
+
+
+@ionit_plugin.function
+def double(value):
+    return 2 * value
+
+
+@ionit_plugin.function
+def example_function():
+    return "Lorem ipsum"
+
+
+def collect_context(current_context):
+    return {"key": "value"}
+```
+
+Prerequisites
+=============
+
+* Python >= 3.4
+* Python modules:
+  * jinja2
+  * yaml or ruamel.yaml
+* pandoc (to generate `ionit.1` man page from `ionit.1.md`)
+
+The test cases have additional requirements:
+
+* flake8
+* pylint
+
+Examples
+========
+
+Static context
+--------------
+
+This example is taken from one test case and demonstrates how ionit will collect
+the context from one JSON and one YAML file and renders one template:
+
+```
+user@host:~/ionit$ cat tests/config/static/first.json
+{"first": 1}
+user@host:~/ionit$ cat tests/config/static/second.yaml
+second: 2
+user@host:~/ionit$ cat tests/template/static/counting.jinja
+Counting:
+* {{ first }}
+* {{ second }}
+* 3
+user@host:~/ionit$ ./ionit -c tests/config/static -t tests/template/static
+2018-08-08 17:39:06,956 ionit INFO: Reading configuration file 'tests/config/static/first.json'...
+2018-08-08 17:39:06,956 ionit INFO: Reading configuration file 'tests/config/static/second.yaml'...
+2018-08-08 17:39:06,960 ionit INFO: Rendered 'tests/template/static/counting.jinja' to 'tests/template/static/counting'.
+user@host:~/ionit$ cat tests/template/static/counting
+Counting:
+* 1
+* 2
+* 3
+```
+
+Python functions
+----------------
+
+This example is taken from one test case and demonstrates how Python functions
+can be defined to be used when rendering:
+
+```
+user@host:~/ionit$ cat tests/config/function/function.py
+import ionit_plugin
+
+
+@ionit_plugin.function
+def answer_to_all_questions():
+    return 42
+user@host:~/ionit$ cat tests/template/function/Document.jinja
+The answer to the Ultimate Question of Life, The Universe, and Everything is {{ answer_to_all_questions() }}.
+user@host:~/ionit$ ./ionit -c tests/config/function -t tests/template/function
+2018-08-13 11:58:16,905 ionit INFO: Loading Python module 'function' from 'tests/config/function/function.py'...
+2018-08-13 11:58:16,909 ionit INFO: Rendered 'tests/template/function/Document.jinja' to 'tests/template/function/Document'.
+user@host:~/ionit$ cat tests/template/function/Document
+The answer to the Ultimate Question of Life, The Universe, and Everything is 42.
+```
+
+Contributing
+============
+
+Contributions are welcome. The source code has 100% test coverage, which should
+be preserved. So please provide a test case for each bugfix and one or more
+test cases for each new feature. Please follow
+[How to Write a Git Commit Message](https://chris.beams.io/posts/git-commit/)
+for writing good commit messages.
diff --git a/ionit b/ionit
new file mode 100755
index 0000000..79d1f35
--- /dev/null
+++ b/ionit
@@ -0,0 +1,208 @@
+#!/usr/bin/python3
+
+# Copyright (C) 2018, Benjamin Drung <benjamin.drung@profitbricks.com>
+#
+# Permission to use, copy, modify, and/or distribute this software for any
+# purpose with or without fee is hereby granted, provided that the above
+# copyright notice and this permission notice appear in all copies.
+#
+# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+# OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+"""Render configuration files from Jinja templates"""
+
+import argparse
+import importlib.util
+import json
+import logging
+import os
+import sys
+
+import jinja2
+import yaml
+
+import ionit_plugin
+
+LOG_FORMAT = '%(asctime)s %(name)s %(levelname)s: %(message)s'
+SCRIPT_NAME = "ionit"
+
+
+class PythonModuleException(Exception):
+    """Exception raised when loading a Python context file fails"""
+    pass
+
+
+def load_python_plugin(file_path, current_context):
+    """Collect context from given Python module
+
+    The specified Python file needs to be a valid plug-in which provides
+    a collect_context function that takes the current context as parameter
+    and returns a dict containing the context.
+    """
+    logger = logging.getLogger(SCRIPT_NAME)
+    module_name = os.path.splitext(os.path.basename(file_path))[0]
+    logger.info("Loading Python module '%s' from '%s'...", module_name, file_path)
+    function_collector = ionit_plugin.FunctionCollector()
+    function_collector.clear()
+    dont_write_bytecode = sys.dont_write_bytecode
+    sys.dont_write_bytecode = True
+    try:
+        if sys.version_info[:2] < (3, 5):
+            # Backwards compatibility for Debian jessie
+            import imp  # pragma: no cover
+            module = imp.load_source(module_name, file_path)  # pragma: no cover
+        else:
+            spec = importlib.util.spec_from_file_location(module_name, file_path)
+            # module_from_spec not available in Python < 3.5.
+            module = importlib.util.module_from_spec(spec)  # pylint: disable=no-member
+            spec.loader.exec_module(module)
+    except Exception:
+        logger.exception("Importing Python module '%s' failed:", file_path)
+        raise PythonModuleException()
+    finally:
+        sys.dont_write_bytecode = dont_write_bytecode
+
+    context = function_collector.functions.copy()
+    if hasattr(module, "collect_context"):
+        try:
+            new_context = module.collect_context(current_context)
+        except Exception:
+            logger.exception("Calling collect_context() from '%s' failed:", file_path)
+            raise PythonModuleException()
+        context.update(new_context)
+
+    if not context:
+        logger.warning("Python module '%s' does neither define a collect_context function, "
+                       "nor export functions (using the ionit_plugin.function decorator).",
+                       file_path)
+
+    return context
+
+
+def collect_context(directory):
+    """Collect context that will be used when rendering the templates"""
+    logger = logging.getLogger(SCRIPT_NAME)
+    logger.debug("Collecting context from '%s'...", directory)
+    try:
+        files = sorted(os.listdir(directory))
+    except OSError as error:
+        logger.warning("Failed to read configuration directory: %s", error)
+        files = []
+
+    failures = 0
+    context = {}
+
+    for filename in files:
+        file_context = None
+        file = os.path.join(directory, filename)
+        extension = os.path.splitext(filename)[1]
+        try:
+            if extension == ".json":
+                logger.info("Reading configuration file '%s'...", file)
+                with open(file) as config_file:
+                    file_context = json.load(config_file)
+            elif extension == ".py":
+                file_context = load_python_plugin(file, context)
+            elif extension == ".yaml":
+                logger.info("Reading configuration file '%s'...", file)
+                with open(file) as config_file:
+                    file_context = yaml.load(config_file)
+            else:
+                logger.info("Skipping configuration file '%s', because it does not end with "
+                            "'.json', '.py', or '.yaml'.", file)
+                continue
+        except PythonModuleException:
+            failures += 1
+            continue
+        except (OSError, ValueError, yaml.error.YAMLError) as error:
+            types = {".json": "JSON", ".py": "Python code", ".yaml": "YAML"}
+            logger.error("Failed to read %s from '%s': %s", types[extension], file, error)
+            failures += 1
+            continue
+
+        logger.debug("Parsed context from '%s': %s", file, file_context)
+        if file_context:
+            try:
+                context.update(file_context)
+            except (TypeError, ValueError) as error:
+                logger.debug("Current context: %s", context)
+                logger.error("Failed to update context with content from '%s': %s",
+                             file, error)
+                failures += 1
+                continue
+
+    return failures, context
+
+
+def render_templates(template_dir, context, template_extension):
+    """
+    Search in the template directory for template files and render them with the context
+    """
+    logger = logging.getLogger(SCRIPT_NAME)
+    logger.debug("Searching in directory '%s' for Jinja templates...", template_dir)
+    failures = 0
+    env = jinja2.Environment(keep_trailing_newline=True,
+                             loader=jinja2.FileSystemLoader(template_dir),
+                             undefined=jinja2.StrictUndefined)
+    for name in env.list_templates(extensions=[template_extension]):
+        try:
+            template = env.get_template(name)
+        except jinja2.TemplateError:
+            logger.exception("Failed to load template '%s':", os.path.join(template_dir, name))
+            failures += 1
+            continue
+
+        rendered_filename = os.path.splitext(template.filename)[0]
+        logger.debug("Rendering template '%s' to '%s'...", template.filename, rendered_filename)
+        try:
+            rendered = template.render(context)
+        except Exception:  # pylint: disable=broad-except
+            logger.exception("Failed to render '%s':", template.filename)
+            failures += 1
+            continue
+
+        try:
+            with open(rendered_filename, "w") as output_file:
+                output_file.write(rendered)
+        except OSError as error:
+            logger.error("Failed to write rendered template to '%s': %s", rendered_filename, error)
+            failures += 1
+            continue
+
+        logger.info("Rendered '%s' to '%s'.", template.filename, rendered_filename)
+
+    return failures
+
+
+def main(argv):
+    """Main function with argument parsing"""
+    parser = argparse.ArgumentParser()
+    parser.add_argument("-c", "--config", default="/etc/ionit",
+                        help="Configuration directory containing context for rendering (default: "
+                             "%(default)s)")
+    parser.add_argument("-t", "--templates", default="/etc",
+                        help="Directory to search for Jinja templates (default: %(default)s)")
+    parser.add_argument("-e", "--template-extension", default="jinja",
+                        help="Extension to look for in template directory (default: %(default)s)")
+    parser.add_argument("--debug", dest="log_level", help="Print debug output",
+                        action="store_const", const=logging.DEBUG, default=logging.INFO)
+    parser.add_argument("-q", "--quiet", dest="log_level",
+                        help="Decrease output verbosity to warnings and errors",
+                        action="store_const", const=logging.WARNING)
+    args = parser.parse_args(argv)
+    logging.basicConfig(level=args.log_level, format=LOG_FORMAT)
+    logger = logging.getLogger(SCRIPT_NAME)
+
+    failures, context = collect_context(args.config)
+    logger.debug("Context: %s", context)
+    failures += render_templates(args.templates, context, args.template_extension)
+    return failures
+
+
+if __name__ == "__main__":
+    sys.exit(main(sys.argv[1:]))  # pragma: no cover
diff --git a/ionit.1.md b/ionit.1.md
new file mode 100644
index 0000000..533ba7c
--- /dev/null
+++ b/ionit.1.md
@@ -0,0 +1,93 @@
+---
+date: 2018-08-13
+footer: ionit
+header: "ionit's Manual"
+layout: page
+license: 'Licensed under the ISC license'
+section: 1
+title: IONIT
+---
+
+# NAME
+
+ionit - Render configuration files from Jinja templates
+
+# SYNOPSIS
+
+**ionit** [**OPTIONS**]
+
+# DESCRIPTION
+
+**ionit** is a simple and small configuration templating tool. It collects a
+context and renders Jinja templates in a given directory. The context can be
+either static JSON or YAML files or dynamic Python files. Python files can also
+define functions passed through to the rendering.
+
+The context filenames needs to end with *.json* for JSON, *.py* for Python,
+and *.yaml* for YAML. The context files are read in alphabetical order. If the
+same key is defined by multiple context files, the file that is read later takes
+precedence. It is recommended to prefix the files with a number in case the
+order is relevant.
+
+**ionit** comes with an early boot one shot service that is executed before the
+networking service which allows one to generate configurations files for the
+networking and other services before they are started. In this regard, ionit can
+act as tiny stepbrother of cloud-init.
+
+# OPTIONS
+
+**-c** */path/to/config*, **--config** */path/to/config*
+:    Configuration directory containing context for rendering (default:
+*/etc/ionit*)
+
+**-t** */path/to/templates*, **--templates** */path/to/templates*
+:    Directory to search for Jinja templates (default: */etc*)
+
+**-e** *TEMPLATE_EXTENSION*, **--template-extension** *TEMPLATE_EXTENSION*
+:    Extension to look for in template directory (default: *jinja*)
+
+**--debug**
+:    Print debug output
+
+**-q**, **--quiet**
+:    Decrease output verbosity to warnings and errors.
+
+# PYTHON MODULES
+
+Python modules can define a *collect_context* function. This function is called
+by ionit and the current context is passed as parameter. The current context can
+be used to derive more context information, but this variable should not be
+modified. *collect_context* must return a dictionary (can be empty) or raise an
+exception, which will be caught by ionit.
+
+Python modules can also define functions which can be called from the Jinja
+template on rendering. Use the *ionit_plugin.function* decorator to mark the
+functions to export.
+
+Note that the functions names should not collide with other keys from the
+context. If one Python module defines a function and a value in the context
+with the same name, the value in the context will take precedence.
+
+An example Python module might look like:
+
+```python
+import ionit_plugin
+
+
+@ionit_plugin.function
+def double(value):
+    return 2 * value
+
+
+@ionit_plugin.function
+def example_function():
+    return "Lorem ipsum"
+
+
+def collect_context(current_context):
+    return {"key": "value"}
+```
+
+# AUTHOR
+
+Benjamin Drung <benjamin.drung@profitbricks.com>
diff --git a/ionit.py b/ionit.py
new file mode 120000
index 0000000..8ce1e53
--- /dev/null
+++ b/ionit.py
@@ -0,0 +1 @@
+ionit
\ No newline at end of file
diff --git a/ionit.service b/ionit.service
new file mode 100644
index 0000000..3da5010
--- /dev/null
+++ b/ionit.service
@@ -0,0 +1,17 @@
+[Unit]
+Description=Render configuration files from Jinja templates
+Documentation=man:ionit(1)
+DefaultDependencies=no
+After=local-fs.target
+Before=network-pre.target openibd.service shutdown.target sysinit.target
+Wants=network-pre.target
+RequiresMountsFor=/usr
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=/usr/bin/ionit
+ExecReload=/usr/bin/ionit
+
+[Install]
+WantedBy=multi-user.target
diff --git a/ionit_plugin.py b/ionit_plugin.py
new file mode 100644
index 0000000..84a9431
--- /dev/null
+++ b/ionit_plugin.py
@@ -0,0 +1,51 @@
+# Copyright (C) 2018, Benjamin Drung <benjamin.drung@profitbricks.com>
+#
+# Permission to use, copy, modify, and/or distribute this software for any
+# purpose with or without fee is hereby granted, provided that the above
+# copyright notice and this permission notice appear in all copies.
+#
+# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+# OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+"""Helper function for writing ionit plugins"""
+
+import logging
+
+
+class FunctionCollector():
+    """Collect functions for the Jinja renderer"""
+    functions = {}
+
+    def __new__(cls):
+        # Singleton
+        if not hasattr(cls, 'instance') or not cls.instance:
+            cls.instance = super().__new__(cls)
+        return cls.instance
+
+    def clear(self):
+        """Reset the list of functions
+
+        Call this method between importing different modules.
+        """
+        self.functions = {}
+
+    def function(self, func):
+        """Function decorator to collect functions for Jinja rendering
+
+        Functions using this decorator will be collected and ionit will
+        use them in the context to make these functions available for
+        the Jinja template rendering.
+
+        """
+        logger = logging.getLogger(__name__)
+        logger.debug("Collecting function '%s'.", func.__name__)
+        self.functions[func.__name__] = func
+        return func
+
+
+function = FunctionCollector().function  # false positive, pylint: disable=invalid-name
diff --git a/setup.py b/setup.py
new file mode 100755
index 0000000..f08401a
--- /dev/null
+++ b/setup.py
@@ -0,0 +1,52 @@
+#!/usr/bin/python3
+
+# Copyright (C) 2018, Benjamin Drung <benjamin.drung@profitbricks.com>
+#
+# Permission to use, copy, modify, and/or distribute this software for any
+# purpose with or without fee is hereby granted, provided that the above
+# copyright notice and this permission notice appear in all copies.
+#
+# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+# OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+"""Setup for ionit"""
+
+import subprocess
+
+from setuptools import setup
+
+
+def systemd_unit_path():
+    """Determine path for systemd units"""
+    try:
+        command = ["pkg-config", "--variable=systemdsystemunitdir", "systemd"]
+        path = subprocess.check_output(command, stderr=subprocess.STDOUT)
+        return path.decode().replace("\n", "")
+    except (subprocess.CalledProcessError, OSError):
+        return "/lib/systemd/system"
+
+
+if __name__ == "__main__":
+    setup(
+        name="ionit",
+        version="0.1",
+        description="Render configuration files from Jinja templates",
+        long_description=(
+            "ionit is a simple and small configuration templating tool. It collects a context and "
+            "renders Jinja templates in a given directory. The context can be either static JSON "
+            "or YAML files or dynamic Python files. Python files can also define functions passed "
+            "through to the rendering."),
+        author="Benjamin Drung",
+        author_email="benjamin.drung@profitbricks.com",
+        url="https://github.com/bdrung/ionit",
+        license="ISC",
+        install_requires=["jinja2"],
+        scripts=["ionit"],
+        py_modules=["ionit_plugin"],
+        data_files=[(systemd_unit_path(), ['ionit.service'])]
+    )
diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 0000000..74c713f
--- /dev/null
+++ b/tests/__init__.py
@@ -0,0 +1,57 @@
+# Copyright (C) 2017, Benjamin Drung <benjamin.drung@profitbricks.com>
+#
+# Permission to use, copy, modify, and/or distribute this software for any
+# purpose with or without fee is hereby granted, provided that the above
+# copyright notice and this permission notice appear in all copies.
+#
+# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+# OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+"""Helper functions for testing ionit"""
+
+import inspect
+import os
+import sys
+import unittest
+
+
+def get_source_files():
+    """Return a list of sources files/directories (to check with flake8/pylint)"""
+    scripts = ["ionit"]
+    modules = ["tests"]
+    py_files = ["ionit_plugin.py", "setup.py"]
+
+    files = []
+    for code_file in scripts + modules + py_files:
+        is_script = code_file in scripts
+        if not os.path.exists(code_file):  # pragma: no cover
+            # The alternative path is needed for Debian's pybuild
+            alternative = os.path.join(os.environ.get("OLDPWD", ""), code_file)
+            code_file = alternative if os.path.exists(alternative) else code_file
+        if is_script:
+            with open(code_file, "rb") as script_file:
+                shebang = script_file.readline().decode("utf-8")
+            if ((sys.version_info[0] == 3 and "python3" in shebang) or
+                    ("python" in shebang and "python3" not in shebang)):
+                files.append(code_file)
+        else:
+            files.append(code_file)
+    return files
+
+
+def unittest_verbosity():
+    """Return the verbosity setting of the currently running unittest
+    program, or None if none is running.
+    """
+    frame = inspect.currentframe()
+    while frame:
+        self = frame.f_locals.get("self")
+        if isinstance(self, unittest.TestProgram):
+            return self.verbosity
+        frame = frame.f_back
+    return None  # pragma: no cover
diff --git a/tests/config/additional-file/echo b/tests/config/additional-file/echo
new file mode 100644
index 0000000..e74b7d4
--- /dev/null
+++ b/tests/config/additional-file/echo
@@ -0,0 +1,2 @@
+#!/bin/sh
+echo "$@"
diff --git a/tests/config/additional-file/valid.yaml b/tests/config/additional-file/valid.yaml
new file mode 100644
index 0000000..b4f46b7
--- /dev/null
+++ b/tests/config/additional-file/valid.yaml
@@ -0,0 +1 @@
+key: value
diff --git a/tests/config/empty/empty.py b/tests/config/empty/empty.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/config/exception/exception.py b/tests/config/exception/exception.py
new file mode 100644
index 0000000..ceaf30e
--- /dev/null
+++ b/tests/config/exception/exception.py
@@ -0,0 +1,2 @@
+def collect_context(_):
+    raise Exception("Oops.")
diff --git a/tests/config/function/function.py b/tests/config/function/function.py
new file mode 100644
index 0000000..b48c162
--- /dev/null
+++ b/tests/config/function/function.py
@@ -0,0 +1,6 @@
+import ionit_plugin
+
+
+@ionit_plugin.function
+def answer_to_all_questions():
+    return 42
diff --git a/tests/config/invalid-json/invalid.json b/tests/config/invalid-json/invalid.json
new file mode 100644
index 0000000..f4db31b
--- /dev/null
+++ b/tests/config/invalid-json/invalid.json
@@ -0,0 +1,3 @@
+{
+	"invalid": "json",
+}
diff --git a/tests/config/invalid-python/invalid.py b/tests/config/invalid-python/invalid.py
new file mode 100644
index 0000000..43e16dd
--- /dev/null
+++ b/tests/config/invalid-python/invalid.py
@@ -0,0 +1 @@
+int("invalid")
diff --git a/tests/config/invalid-yaml/invalid.yaml b/tests/config/invalid-yaml/invalid.yaml
new file mode 100644
index 0000000..63fa846
--- /dev/null
+++ b/tests/config/invalid-yaml/invalid.yaml
@@ -0,0 +1 @@
+invalid: yaml: file
diff --git a/tests/config/non-dict/invalid.yaml b/tests/config/non-dict/invalid.yaml
new file mode 100644
index 0000000..276760c
--- /dev/null
+++ b/tests/config/non-dict/invalid.yaml
@@ -0,0 +1 @@
+this-is-not-a-dictionary
diff --git a/tests/config/python/number.py b/tests/config/python/number.py
new file mode 100644
index 0000000..fd5ac63
--- /dev/null
+++ b/tests/config/python/number.py
@@ -0,0 +1,5 @@
+def collect_context(_):
+    return {
+        "small": 42,
+        "big": 8000,
+    }
diff --git a/tests/config/stacking/first.yaml b/tests/config/stacking/first.yaml
new file mode 100644
index 0000000..6077bd8
--- /dev/null
+++ b/tests/config/stacking/first.yaml
@@ -0,0 +1 @@
+small_number: 7
diff --git a/tests/config/stacking/second.py b/tests/config/stacking/second.py
new file mode 100644
index 0000000..f404a22
--- /dev/null
+++ b/tests/config/stacking/second.py
@@ -0,0 +1,2 @@
+def collect_context(current_context):
+    return {"big_number": current_context["small_number"] * 153}
diff --git a/tests/config/static/first.json b/tests/config/static/first.json
new file mode 100644
index 0000000..cb0ed06
--- /dev/null
+++ b/tests/config/static/first.json
@@ -0,0 +1 @@
+{"first": 1}
diff --git a/tests/config/static/second.yaml b/tests/config/static/second.yaml
new file mode 100644
index 0000000..0ac734c
--- /dev/null
+++ b/tests/config/static/second.yaml
@@ -0,0 +1 @@
+second: 2
diff --git a/tests/mock_open.py b/tests/mock_open.py
new file mode 100644
index 0000000..ae5acc2
--- /dev/null
+++ b/tests/mock_open.py
@@ -0,0 +1,97 @@
+# The MIT License (MIT)
+
+# Copyright (c) 2013 Ionuț Arțăriși <ionut@artarisi.eu>
+#               2018 Benjamin Drung <benjamin.drung@profitbricks.com>
+
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+
+# The above copyright notice and this permission notice shall be included in
+# all copies or substantial portions of the Software.
+
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+# THE SOFTWARE.
+
+"""Helper function to mock the builtin open() function
+
+Origin: https://github.com/mapleoin/mock_open
+"""
+
+
+import contextlib
+import io
+import unittest.mock
+
+
+class NotMocked(Exception):
+    """Raised when a file was opened which was not mocked"""
+    def __init__(self, filename):
+        super(NotMocked, self).__init__(
+            "The file %s was opened, but not mocked." % filename)
+        self.filename = filename
+
+
+@contextlib.contextmanager
+def mock_open(filename, contents=None, exception=None, complain=True):
+    """Mock the open() builtin function on a specific filename
+
+    Let execution pass through to open() on files different than
+    :filename:. Return a StringIO with :contents: if the file was
+    matched. If the :contents: parameter is not given or if it is None,
+    a StringIO instance simulating an empty file is returned.
+
+    If :exception: is defined, this Exception will be raised when
+    open is called instead of returning the :contents:.
+
+    If :complain: is True (default), will raise an AssertionError if
+    :filename: was not opened in the enclosed block. A NotMocked
+    exception will be raised if open() was called with a file that was
+    not mocked by mock_open.
+
+    """
+    open_files = set()
+
+    def mock_file(*args):
+        """Mocked open() function
+
+        Takes the same arguments as the open() function.
+
+        """
+        if args[0] == filename:
+            if exception is None:
+                file_ = io.StringIO(contents)
+                file_.name = filename
+            else:
+                raise exception  # false positive; pylint: disable=raising-bad-type
+        else:
+            mocked_file.stop()
+            file_ = open(*args)
+            mocked_file.start()
+        open_files.add(file_.name)
+        return file_
+
+    mocked_file = unittest.mock.patch('builtins.open', mock_file)
+    mocked_file.start()
+    try:
+        yield
+    except NotMocked as error:
+        if error.filename != filename:
+            raise
+    mocked_file.stop()
+    try:
+        open_files.remove(filename)
+    except KeyError:
+        if complain:
+            raise AssertionError("The file %s was not opened." % filename)
+    for f_name in open_files:
+        if complain:
+            raise NotMocked(f_name)
diff --git a/tests/pylint.conf b/tests/pylint.conf
new file mode 100644
index 0000000..709bb5b
--- /dev/null
+++ b/tests/pylint.conf
@@ -0,0 +1,30 @@
+[MASTER]
+
+# Pickle collected data for later comparisons.
+persistent=no
+
+
+[MESSAGES CONTROL]
+
+# Disable the message, report, category or checker with the given id(s). You
+# can either give multiple identifiers separated by comma (,) or put this
+# option multiple times (only on the command line, not in the configuration
+# file where it should appear only once).You can also use "--disable=all" to
+# disable everything first and then reenable specific checks. For example, if
+# you want to run only the similarities checker, you can use "--disable=all
+# --enable=similarities". If you want to run only the classes checker, but have
+# no Warning level messages displayed, use"--disable=all --enable=classes
+# --disable=W"
+disable=fixme,locally-enabled,locally-disabled
+
+
+[REPORTS]
+
+# Tells whether to display a full report or only the messages
+reports=no
+
+
+[FORMAT]
+
+# Maximum number of characters on a single line.
+max-line-length=99
diff --git a/tests/template/attribution-error/error.jinja b/tests/template/attribution-error/error.jinja
new file mode 100644
index 0000000..e9a6c54
--- /dev/null
+++ b/tests/template/attribution-error/error.jinja
@@ -0,0 +1,4 @@
+{% set mapping = {1: "one"} %}
+{% for number, string in mapping.items()|dictsort %}
+A number: {{ string }}
+{% endfor %}
diff --git a/tests/template/function/Document.jinja b/tests/template/function/Document.jinja
new file mode 100644
index 0000000..cf4d02c
--- /dev/null
+++ b/tests/template/function/Document.jinja
@@ -0,0 +1 @@
+The answer to the Ultimate Question of Life, The Universe, and Everything is {{ answer_to_all_questions() }}.
diff --git a/tests/template/invalid/invalid.jinja b/tests/template/invalid/invalid.jinja
new file mode 100644
index 0000000..7292b93
--- /dev/null
+++ b/tests/template/invalid/invalid.jinja
@@ -0,0 +1,2 @@
+# Cause a loading failure!
+{{
diff --git a/tests/template/static/counting.jinja b/tests/template/static/counting.jinja
new file mode 100644
index 0000000..87711d2
--- /dev/null
+++ b/tests/template/static/counting.jinja
@@ -0,0 +1,4 @@
+Counting:
+* {{ first }}
+* {{ second }}
+* 3
diff --git a/tests/test_flake8.py b/tests/test_flake8.py
new file mode 100644
index 0000000..63f65e1
--- /dev/null
+++ b/tests/test_flake8.py
@@ -0,0 +1,51 @@
+# Copyright (C) 2017-2018, Benjamin Drung <bdrung@debian.org>
+#
+# Permission to use, copy, modify, and/or distribute this software for any
+# purpose with or without fee is hereby granted, provided that the above
+# copyright notice and this permission notice appear in all copies.
+#
+# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+# OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+"""test_flake8.py - Run flake8 check"""
+
+import subprocess
+import sys
+import unittest
+
+from . import get_source_files, unittest_verbosity
+
+
+class Flake8TestCase(unittest.TestCase):
+    """
+    This unittest class provides a test that runs the flake8 code
+    checker (which combines pycodestyle and pyflakes) on the Python
+    source code. The list of source files is provided by the
+    get_source_files() function.
+    """
+
+    def test_flake8(self):
+        """Test: Run flake8 on Python source code"""
+        cmd = [sys.executable, "-m", "flake8", "--max-line-length=99"] + get_source_files()
+        if unittest_verbosity() >= 2:
+            sys.stderr.write("Running following command:\n{}\n".format(" ".join(cmd)))
+        process = subprocess.Popen(cmd, stdout=subprocess.PIPE,
+                                   stderr=subprocess.PIPE, close_fds=True)
+
+        out, err = process.communicate()
+        if process.returncode != 0:  # pragma: no cover
+            msgs = []
+            if err:
+                msgs.append("flake8 exited with code {} and has unexpected output on stderr:\n{}"
+                            .format(process.returncode, err.decode().rstrip()))
+            if out:
+                msgs.append("flake8 found issues:\n{}".format(out.decode().rstrip()))
+            if not msgs:
+                msgs.append("flake8 exited with code {} and has no output on stdout or stderr."
+                            .format(process.returncode))
+            self.fail("\n".join(msgs))
diff --git a/tests/test_ionit.py b/tests/test_ionit.py
new file mode 100644
index 0000000..eb41ecb
--- /dev/null
+++ b/tests/test_ionit.py
@@ -0,0 +1,231 @@
+# Copyright (C) 2018, Benjamin Drung <benjamin.drung@profitbricks.com>
+#
+# Permission to use, copy, modify, and/or distribute this software for any
+# purpose with or without fee is hereby granted, provided that the above
+# copyright notice and this permission notice appear in all copies.
+#
+# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+# REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+# AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+# INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+# LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+# OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+# PERFORMANCE OF THIS SOFTWARE.
+
+"""Test ionit"""
+
+import os
+import re
+import unittest
+
+from ionit import collect_context, main, render_templates
+
+from .mock_open import mock_open
+
+TESTS_DIR = os.path.abspath(os.path.dirname(__file__))
+CONFIG_DIR = os.path.join(TESTS_DIR, "config")
+TEMPLATE_DIR = os.path.join(TESTS_DIR, "template")
+
+
+class TestCollectContext(unittest.TestCase):
+    """
+    This unittest class tests collecting the context.
+    """
+
+    def test_collect_function(self):
+        """Test: Run collect_context("tests/config/function")"""
+        failures, context = collect_context(os.path.join(CONFIG_DIR, "function"))
+        self.assertEqual(failures, 0)
+        self.assertEqual(set(context.keys()), set(["answer_to_all_questions"]))
+        self.assertEqual(context["answer_to_all_questions"](), 42)
+
+    def test_collect_static_context(self):
+        """Test: Run collect_context("tests/config/static")"""
+        self.assertEqual(collect_context(os.path.join(CONFIG_DIR, "static")), (0, {
+            "first": 1,
+            "second": 2,
+        }))
+
+    def test_context_stacking(self):
+        """Test: Run collect_context("tests/config/stacking")"""
+        self.assertEqual(collect_context(os.path.join(CONFIG_DIR, "stacking")), (0, {
+            "big_number": 1071,
+            "small_number": 7,
+        }))
+
+    def test_empty_python_file(self):
+        """Test: Run collect_context("tests/config/empty")"""
+        with self.assertLogs("ionit", level="WARNING") as context_manager:
+            self.assertEqual(collect_context(os.path.join(CONFIG_DIR, "empty")), (0, {}))
+            self.assertEqual(len(context_manager.output), 1)
+            self.assertRegex(context_manager.output[0], (
+                "WARNING:ionit:Python module '[^']+config/empty/empty.py' does "
+                "neither define a collect_context function, nor export functions "
+                r"\(using the ionit_plugin.function decorator\)."))
+
+    def test_ignoring_additional_files(self):
+        """Test: Run collect_context("tests/config/additional-file")"""
+        with self.assertLogs("ionit", level="INFO") as context_manager:
+            self.assertEqual(collect_context(os.path.join(CONFIG_DIR, "additional-file")),
+                             (0, {"key": "value"}))
+            self.assertEqual(len(context_manager.output), 2)
+            self.assertRegex(context_manager.output[0], (
+                "INFO:ionit:Skipping configuration file '[^']*config/additional-file/echo', "
+                "because it does not end with .*"))
+
+    def test_invalid_json(self):
+        """Test: Run collect_context("tests/config/invalid-json")"""
+        with self.assertLogs("ionit", level="ERROR") as context_manager:
+            self.assertEqual(collect_context(os.path.join(CONFIG_DIR, "invalid-json")), (1, {}))
+            self.assertEqual(len(context_manager.output), 1)
+            self.assertRegex(context_manager.output[0], (
+                "ERROR:ionit:Failed to read JSON from '[^']*config/invalid-json/invalid.json': "
+                r"Expecting property name enclosed in double quotes: line 3 column 1 \(char 22\)"))
+
+    def test_invalid_python(self):
+        """Test: Run collect_context("tests/config/invalid-python")"""
+        with self.assertLogs("ionit", level="ERROR") as context_manager:
+            self.assertEqual(collect_context(os.path.join(CONFIG_DIR, "invalid-python")), (1, {}))
+            self.assertEqual(len(context_manager.output), 1)
+            self.assertRegex(context_manager.output[0], re.compile(
+                "ERROR:ionit:Importing Python module '[^']*config/invalid-python/invalid.py' "
+                r"failed:\n.*\nValueError: invalid literal for int\(\) with base 10: 'invalid'$",
+                flags=re.DOTALL))
+
+    def test_invalid_yaml(self):
+        """Test: Run collect_context("tests/config/invalid-yaml")"""
+        with self.assertLogs("ionit", level="ERROR") as context_manager:
+            self.assertEqual(collect_context(os.path.join(CONFIG_DIR, "invalid-yaml")), (1, {}))
+            self.assertEqual(len(context_manager.output), 1)
+            self.assertRegex(context_manager.output[0], (
+                "ERROR:ionit:Failed to read YAML from '[^']*config/invalid-yaml/invalid.yaml': "
+                r"mapping values are not allowed here\s+"
+                r"in \"\S*config/invalid-yaml/invalid.yaml\", line 1, column 14"))
+
+    def test_missing_directory(self):
+        """Test: Non-existing context directory"""
+        with self.assertLogs("ionit", level="WARNING") as context_manager:
+            self.assertEqual(collect_context(os.path.join(TESTS_DIR, "non-existing-directory")),
+                             (0, {}))
+            self.assertEqual(len(context_manager.output), 1)
+            self.assertRegex(context_manager.output[0], (
+                r"WARNING:ionit:Failed to read configuration directory: \[Errno 2\] "
+                r"No such file or directory: '\S*non-existing-directory'"))
+
+    def test_non_dict_context(self):
+        """Test failure for collect_context("tests/config/non-dict")"""
+        with self.assertLogs("ionit", level="ERROR") as context_manager:
+            self.assertEqual(collect_context(os.path.join(CONFIG_DIR, "non-dict")), (1, {}))
+            self.assertEqual(len(context_manager.output), 1)
+            self.assertRegex(context_manager.output[0], (
+                "ERROR:ionit:Failed to update context with content from "
+                r"'\S*config/non-dict/invalid.yaml': dictionary update sequence "
+                "element #0 has length 1; 2 is required"))
+
+    def test_python_module(self):
+        """Test: Run collect_context("tests/config/python")"""
+        self.assertEqual(collect_context(os.path.join(CONFIG_DIR, "python")), (0, {
+            "small": 42,
+            "big": 8000,
+        }))
+
+    def test_raise_exception(self):
+        """Test failure for collect_context("tests/config/exception")"""
+        with self.assertLogs("ionit", level="ERROR") as context_manager:
+            self.assertEqual(collect_context(os.path.join(CONFIG_DIR, "exception")), (1, {}))
+            self.assertEqual(len(context_manager.output), 1)
+            self.assertRegex(context_manager.output[0], re.compile(
+                r"ERROR:ionit:Calling collect_context\(\) from '\S*config/exception/exception.py' "
+                "failed:\n.*\nException: Oops.$", flags=re.DOTALL))
+
+
+class TestRendering(unittest.TestCase):
+    """
+    This unittest class tests rendering the templates.
+    """
+
+    def test_attribution_error(self):
+        """Test: Run render_templates("tests/template/attribution-error")"""
+        template_dir = os.path.join(TEMPLATE_DIR, "attribution-error")
+        with self.assertLogs("ionit", level="ERROR") as context_manager:
+            self.assertEqual(render_templates(template_dir, {}, "jinja"), 1)
+            self.assertFalse(os.path.exists(os.path.join(template_dir, "error")))
+            self.assertEqual(len(context_manager.output), 1)
+            self.assertRegex(context_manager.output[0], re.compile(
+                r"^ERROR:ionit:Failed to render '\S*template/attribution-error/error.jinja':\n.*\n"
+                "AttributeError: 'dict_items' object has no attribute 'items'$", flags=re.DOTALL))
+
+    def test_missing_context(self):
+        """Test: Missing context for render_templates("tests/template/static")"""
+        template_dir = os.path.join(TEMPLATE_DIR, "static")
+        with self.assertLogs("ionit", level="ERROR") as context_manager:
+            self.assertEqual(render_templates(template_dir, {"second": "B"}, "jinja"), 1)
+            self.assertFalse(os.path.exists(os.path.join(template_dir, "counting")))
+            self.assertEqual(len(context_manager.output), 1)
+            self.assertRegex(context_manager.output[0], re.compile(
+                r"^ERROR:ionit:Failed to render '\S*template/static/counting.jinja':\n.*\n"
+                "jinja2.exceptions.UndefinedError: 'first' is undefined$", flags=re.DOTALL))
+
+    def test_render_function(self):
+        """Test: Run render_templates("tests/template/function")"""
+        template_dir = os.path.join(TEMPLATE_DIR, "function")
+        try:
+            context = {"answer_to_all_questions": lambda: 42}
+            self.assertEqual(render_templates(template_dir, context, "jinja"), 0)
+            with open(os.path.join(template_dir, "Document")) as document_file:
+                self.assertEqual(document_file.read(), (
+                    "The answer to the Ultimate Question of Life, The Universe, "
+                    "and Everything is 42.\n"))
+        finally:
+            os.remove(os.path.join(template_dir, "Document"))
+
+    def test_render_invalid(self):
+        """Test: Run render_templates("tests/template/invalid")"""
+        template_dir = os.path.join(TEMPLATE_DIR, "invalid")
+        with self.assertLogs("ionit", level="ERROR") as context_manager:
+            self.assertEqual(render_templates(template_dir, {}, "jinja"), 1)
+            self.assertFalse(os.path.exists(os.path.join(template_dir, "invalid")))
+            self.assertEqual(len(context_manager.output), 1)
+            self.assertRegex(context_manager.output[0], re.compile(
+                r"ERROR:ionit:Failed to load template '\S*template/invalid/invalid.jinja':\n.*\n"
+                "jinja2.exceptions.TemplateSyntaxError: unexpected 'end of template'$",
+                flags=re.DOTALL))
+
+    def test_render_static(self):
+        """Test: Run render_templates("tests/template/static")"""
+        template_dir = os.path.join(TEMPLATE_DIR, "static")
+        try:
+            context = {"first": "A", "second": "B"}
+            self.assertEqual(render_templates(template_dir, context, "jinja"), 0)
+            with open(os.path.join(template_dir, "counting")) as counting_file:
+                self.assertEqual(counting_file.read(), "Counting:\n* A\n* B\n* 3\n")
+        finally:
+            os.remove(os.path.join(template_dir, "counting"))
+
+    def test_render_write_protected(self):
+        """Test: Run render_templates("tests/template/static"), but write protected"""
+        template_dir = os.path.join(TEMPLATE_DIR, "static")
+        context = {"first": "A", "second": "B"}
+        with self.assertLogs("ionit", level="ERROR") as context_manager:
+            with mock_open(os.path.join(template_dir, "counting"),
+                           exception=PermissionError(13, "Permission denied"), complain=False):
+                self.assertEqual(render_templates(template_dir, context, "jinja"), 1)
+            self.assertFalse(os.path.exists(os.path.join(template_dir, "counting")))
+            self.assertEqual(len(context_manager.output), 1)
+            self.assertRegex(context_manager.output[0], (
+                r"ERROR:ionit:Failed to write rendered template to '\S*template/static/counting': "
+                r"\[Errno 13\] Permission denied"))
+
+
+class TestMain(unittest.TestCase):
+    """Test main function"""
+    def test_main_static(self):
+        """Test main() with static context"""
+        template_dir = os.path.join(TEMPLATE_DIR, "static")
+        try:
+            self.assertEqual(main(["-c", os.path.join(TESTS_DIR, "config/static"), "-t",
+                                   template_dir]), 0)
+            with open(os.path.join(template_dir, "counting")) as counting_file:
+                self.assertEqual(counting_file.read(), "Counting:\n* 1\n* 2\n* 3\n")
+        finally:
+            os.remove(os.path.join(template_dir, "counting"))
diff --git a/tests/test_mock_open.py b/tests/test_mock_open.py
new file mode 100644
index 0000000..3d855bf
--- /dev/null
+++ b/tests/test_mock_open.py
@@ -0,0 +1,75 @@
+# The MIT License (MIT)
+
+# Copyright (c) 2013 Ionuț Arțăriși <ionut@artarisi.eu>
+
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+
+# The above copyright notice and this permission notice shall be included in
+# all copies or substantial portions of the Software.
+
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+# THE SOFTWARE.
+
+"""Test mock_open()
+
+Origin: https://github.com/mapleoin/mock_open
+"""
+
+import collections
+import unittest
+import unittest.mock
+
+from .mock_open import NotMocked, mock_open
+
+
+class OrderedSet(collections.UserList):  # pylint: disable=too-many-ancestors
+    """set subclass that remembers the order entries were added"""
+    def add(self, element):
+        """Add given element to set"""
+        if element not in self.data:
+            self.data.append(element)
+
+
+class MockTest(unittest.TestCase):
+    """Test mock_open()"""
+    def test_open_same_file_twice(self):
+        """Test opening the same mocked file twice"""
+        with mock_open("test_file", "foo"):
+            with open("test_file") as first:
+                with open("test_file") as second:
+                    self.assertEqual(first.read(), second.read())
+                    first.seek(0)
+                    self.assertEqual("foo", first.read())
+
+    def test_file_not_open_mocked(self):
+        """Test not opening the mocked file"""
+        with self.assertRaises(AssertionError):
+            with mock_open("file"):
+                pass
+
+    @unittest.mock.patch("builtins.set", OrderedSet)
+    def test_file_open_not_mocked(self):
+        """Test opening a not mocked file"""
+        with self.assertRaises(NotMocked):
+            with mock_open("file1", "foo"):
+                with mock_open("file2", "foo"):
+                    with open(__file__):
+                        with open("file1") as mocked_file1:
+                            with open("file2") as mocked_file2:
+                                self.assertEqual(mocked_file1.read(), mocked_file2.read())
+
+    def test_raise_exception(self):
+        """Test raising an exception on mocked open()"""
+        with self.assertRaises(PermissionError):
+            with mock_open("file", exception=PermissionError(13, "Permission denied")):
+                open("file")
diff --git a/tests/test_pylint.py b/tests/test_pylint.py
new file mode 100644
index 0000000..ac08fda
--- /dev/null
+++ b/tests/test_pylint.py
@@ -0,0 +1,68 @@
+# Copyright (C) 2010, Stefano Rivera <stefanor@debian.org>
+# Copyright (C) 2017-2018, Benjamin Drung <bdrung@debian.org>
+#
+# Permission to use, copy, modify, and/or distribute this software for any
+# purpose with or without fee is hereby granted, provided that the above
+# copyright notice and this permission notice appear in all copies.
+#
+# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+# REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+# AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+# INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+# LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+# OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+# PERFORMANCE OF THIS SOFTWARE.
+
+"""test_pylint.py - Run pylint"""
+
+import os
+import re
+import subprocess
+import sys
+import unittest
+
+from . import get_source_files, unittest_verbosity
+
+CONFIG = os.path.join(os.path.dirname(__file__), "pylint.conf")
+
+
+class PylintTestCase(unittest.TestCase):
+    """
+    This unittest class provides a test that runs the pylint code check
+    on the Python source code. The list of source files is provided by
+    the get_source_files() function and pylint is purely configured via
+    a config file.
+    """
+
+    def test_pylint(self):
+        """Test: Run pylint on Python source code"""
+
+        cmd = [sys.executable, "-m", "pylint", "--rcfile=" + CONFIG, "--"] + get_source_files()
+        if unittest_verbosity() >= 2:
+            sys.stderr.write("Running following command:\n{}\n".format(" ".join(cmd)))
+        process = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE,
+                                   close_fds=True)
+        out, err = process.communicate()
+
+        if process.returncode != 0:  # pragma: no cover
+            # Strip trailing summary (introduced in pylint 1.7). This summary might look like:
+            #
+            # ------------------------------------
+            # Your code has been rated at 10.00/10
+            #
+            out = re.sub("^(-+|Your code has been rated at .*)$", "", out.decode(),
+                         flags=re.MULTILINE).rstrip()
+
+            # Strip logging of used config file (introduced in pylint 1.8)
+            err = re.sub("^Using config file .*\n", "", err.decode()).rstrip()
+
+            msgs = []
+            if err:
+                msgs.append("pylint exited with code {} and has unexpected output on stderr:\n{}"
+                            .format(process.returncode, err))
+            if out:
+                msgs.append("pylint found issues:\n{}".format(out))
+            if not msgs:
+                msgs.append("pylint exited with code {} and has no output on stdout or stderr."
+                            .format(process.returncode))
+            self.fail("\n".join(msgs))