diff --git a/CHANGES.rst b/CHANGES.rst
index 62880976..90cf1c9b 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -63,6 +63,7 @@ New features:
 
 - icalendar utility outputs a 'Duration' row
 - icalendar can take multiple ics files as an input
+- source code in documentation is tested using doctest #445 [niccokunzmann]
 
 Bug fixes:
 
diff --git a/docs/install.rst b/docs/install.rst
index eb1afb14..cc938c53 100644
--- a/docs/install.rst
+++ b/docs/install.rst
@@ -112,7 +112,7 @@ Try it out:
     Type "help", "copyright", "credits" or "license" for more information.
     >>> import icalendar
     >>> icalendar.__version__
-    '4.0.10.dev0'
+    '5.0.1'
 
 Building the documentation locally
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
diff --git a/docs/maintenance.rst b/docs/maintenance.rst
index 2313ac43..6fb7460e 100644
--- a/docs/maintenance.rst
+++ b/docs/maintenance.rst
@@ -56,7 +56,10 @@ However, only people with ``PyPI environment access for GitHub Actions`` can app
 
 1. Check that the ``CHANGES.rst`` is up to date with the `latest merged pull requests <https://github.com/collective/icalendar/pulls?q=is%3Apr+is%3Amerged>`__
    and the version you want to release is correctly named.
-2. Change the ``__version__`` variable in the ``src/icalendar/__init__.py`` file.
+2. Change the ``__version__`` variable in
+
+   - the ``src/icalendar/__init__.py`` file and 
+   - in the ``docs/usage.rst`` file (look for ``icalendar.__version__``)
 3. Create a commit on the ``release-5.0.0`` branch (or equivalent) to release this version.
 
    .. code-block:: bash
diff --git a/docs/usage.rst b/docs/usage.rst
index 48b6e9b7..63786714 100644
--- a/docs/usage.rst
+++ b/docs/usage.rst
@@ -79,8 +79,8 @@ you do it like this. The calendar is a component::
   >>> cal['summary'] = 'Python meeting about calendaring'
   >>> for k,v in cal.items():
   ...     k,v
-  (u'DTSTART', '20050404T080000')
-  (u'SUMMARY', 'Python meeting about calendaring')
+  ('DTSTART', '20050404T080000')
+  ('SUMMARY', 'Python meeting about calendaring')
 
 NOTE: the recommended way to add components to the calendar is to use
 create the subcomponent and add it via Calendar.add! The example above adds a
@@ -90,7 +90,7 @@ string, but not a vText component.
 You can generate a string for a file with the to_ical() method::
 
   >>> cal.to_ical()
-  'BEGIN:VCALENDAR\r\nDTSTART:20050404T080000\r\nSUMMARY:Python meeting about calendaring\r\nEND:VCALENDAR\r\n'
+  b'BEGIN:VCALENDAR\r\nDTSTART:20050404T080000\r\nSUMMARY:Python meeting about calendaring\r\nEND:VCALENDAR\r\n'
 
 The rendered view is easier to read::
 
@@ -102,13 +102,13 @@ The rendered view is easier to read::
 So, let's define a function so we can easily display to_ical() output::
 
   >>> def display(cal):
-  ...    return cal.to_ical().decode("utf-8").replace(b'\r\n', b'\n').strip()
+  ...    return cal.to_ical().decode("utf-8").replace('\r\n', '\n').strip()
 
 You can set multiple properties like this::
 
   >>> cal = Calendar()
   >>> cal['attendee'] = ['MAILTO:maxm@mxm.dk','MAILTO:test@example.com']
-  >>> print display(cal)
+  >>> print(display(cal))
   BEGIN:VCALENDAR
   ATTENDEE:MAILTO:maxm@mxm.dk
   ATTENDEE:MAILTO:test@example.com
@@ -122,7 +122,7 @@ added. Here is an example::
   >>> cal = Calendar()
   >>> cal.add('attendee', 'MAILTO:maxm@mxm.dk')
   >>> cal.add('attendee', 'MAILTO:test@example.com')
-  >>> print display(cal)
+  >>> print(display(cal))
   BEGIN:VCALENDAR
   ATTENDEE:MAILTO:maxm@mxm.dk
   ATTENDEE:MAILTO:test@example.com
@@ -148,7 +148,7 @@ component::
 And then appending it to a "parent"::
 
   >>> cal.add_component(event)
-  >>> print display(cal)
+  >>> print(display(cal))
   BEGIN:VCALENDAR
   ATTENDEE:MAILTO:maxm@mxm.dk
   ATTENDEE:MAILTO:test@example.com
@@ -161,7 +161,7 @@ And then appending it to a "parent"::
 Subcomponents are appended to the subcomponents property on the component::
 
   >>> cal.subcomponents
-  [VEVENT({'DTSTART': '20050404T080000', 'UID': '42'})]
+  [VEVENT({'UID': '42', 'DTSTART': '20050404T080000'})]
 
 
 Value types
@@ -184,7 +184,7 @@ type defined in the spec::
   >>> from datetime import datetime
   >>> cal.add('dtstart', datetime(2005,4,4,8,0,0))
   >>> cal['dtstart'].to_ical()
-  '20050404T080000'
+  b'20050404T080000'
 
 If that doesn't work satisfactorily for some reason, you can also do it
 manually.
@@ -197,7 +197,7 @@ So if you want to do it manually::
   >>> from icalendar import vDatetime
   >>> now = datetime(2005,4,4,8,0,0)
   >>> vDatetime(now).to_ical()
-  '20050404T080000'
+  b'20050404T080000'
 
 So the drill is to initialise the object with a python built in type,
 and then call the "to_ical()" method on the object. That will return an
@@ -220,7 +220,7 @@ value directly::
   >>> cal = Calendar()
   >>> cal.add('dtstart', datetime(2005,4,4,8,0,0))
   >>> cal['dtstart'].to_ical()
-  '20050404T080000'
+  b'20050404T080000'
   >>> cal.decoded('dtstart')
   datetime.datetime(2005, 4, 4, 8, 0)
 
@@ -232,12 +232,13 @@ Property parameters are automatically added, depending on the input value. For
 example, for date/time related properties, the value type and timezone
 identifier (if applicable) are automatically added here::
 
+    >>> import pytz
     >>> event = Event()
     >>> event.add('dtstart', datetime(2010, 10, 10, 10, 0, 0,
     ...                               tzinfo=pytz.timezone("Europe/Vienna")))
 
     >>> lines = event.to_ical().splitlines()
-    >>> self.assertTrue(
+    >>> assert (
     ...     b"DTSTART;TZID=Europe/Vienna;VALUE=DATE-TIME:20101010T100000"
     ...     in lines)
 
@@ -247,9 +248,9 @@ dictionary to the add method like so::
 
     >>> event = Event()
     >>> event.add('X-TEST-PROP', 'tryout.',
-    ....          parameters={'prop1': 'val1', 'prop2': 'val2'})
+    ...           parameters={'prop1':'val1', 'prop2':'val2'})
     >>> lines = event.to_ical().splitlines()
-    >>> self.assertTrue(b"X-TEST-PROP;PROP1=val1;PROP2=val2:tryout." in lines)
+    >>> assert b"X-TEST-PROP;PROP1=val1;PROP2=val2:tryout." in lines
 
 
 Example
@@ -270,7 +271,6 @@ Some properties are required to be compliant::
 
 We need at least one subcomponent for a calendar to be compliant::
 
-  >>> import pytz
   >>> event = Event()
   >>> event.add('summary', 'Python meeting about calendaring')
   >>> event.add('dtstart', datetime(2005,4,4,8,0,0,tzinfo=pytz.utc))
@@ -314,6 +314,7 @@ Write to disk::
   >>> directory = tempfile.mkdtemp()
   >>> f = open(os.path.join(directory, 'example.ics'), 'wb')
   >>> f.write(cal.to_ical())
+  570
   >>> f.close()
 
 
diff --git a/src/icalendar/tests/test_with_doctest.py b/src/icalendar/tests/test_with_doctest.py
new file mode 100644
index 00000000..652198c3
--- /dev/null
+++ b/src/icalendar/tests/test_with_doctest.py
@@ -0,0 +1,67 @@
+"""This file tests the source code provided by the documentation.
+
+See 
+- doctest documentation: https://docs.python.org/3/library/doctest.html
+- Issue 443: https://github.com/collective/icalendar/issues/443
+
+This file should be tests, too:
+
+    >>> print("Hello World!")
+    Hello World!
+
+"""
+import doctest
+import os
+import pytest
+import importlib
+
+HERE = os.path.dirname(__file__) or "."
+ICALENDAR_PATH = os.path.dirname(HERE)
+
+PYTHON_FILES = [
+    os.path.join(dirpath, filename)
+    for dirpath, dirnames, filenames in os.walk(ICALENDAR_PATH)
+    for filename in filenames if filename.lower().endswith(".py")
+]
+
+MODULE_NAMES = [
+    "icalendar" + python_file[len(ICALENDAR_PATH):-3].replace("/", ".")
+    for python_file in PYTHON_FILES
+]
+
+def test_this_module_is_among_them():
+    assert __name__ in MODULE_NAMES
+
+@pytest.mark.parametrize("module_name", MODULE_NAMES)
+def test_docstring_of_python_file(module_name):
+    """This test runs doctest on the Python module."""
+    module = importlib.import_module(module_name)
+    test_result = doctest.testmod(module, name=module_name)
+    assert test_result.failed == 0, f"{test_result.failed} errors in {module_name}"
+
+
+# This collection needs to exclude .tox and other subdirectories
+DOCUMENTATION_PATH = os.path.join(HERE, "../../../")
+
+DOCUMENT_PATHS = [
+    os.path.join(DOCUMENTATION_PATH, subdir, filename)
+    for subdir in ["docs", "."]
+    for filename in os.listdir(os.path.join(DOCUMENTATION_PATH, subdir))
+    if filename.lower().endswith(".rst")
+]
+
+@pytest.mark.parametrize("filename", [
+    "README.rst",
+    "index.rst",
+])
+def test_files_is_included(filename):
+    assert any(path.endswith(filename) for path in DOCUMENT_PATHS)
+
+@pytest.mark.parametrize("document", DOCUMENT_PATHS)
+def test_documentation_file(document):
+    """This test runs doctest on a documentation file."""
+    test_result = doctest.testfile(document, module_relative=False)
+    assert test_result.failed == 0, f"{test_result.failed} errors in {os.path.basename(document)}"
+
+
+
diff --git a/tox.ini b/tox.ini
index 30a56afc..3a13fd5c 100644
--- a/tox.ini
+++ b/tox.ini
@@ -10,6 +10,7 @@ usedevelop=True
 deps =
     pytest
     coverage
+    hypothesis
 commands =
     coverage run --source=src/icalendar --omit=*/tests/* --module pytest []
     coverage report