diff --git a/.coveragerc b/.coveragerc
new file mode 100644
index 00000000..1b2271b9
--- /dev/null
+++ b/.coveragerc
@@ -0,0 +1,8 @@
+[run]
+branch = true
+parallel = true
+source =
+    telethon
+
+[report]
+precision = 2
diff --git a/.github/workflows/python.yml b/.github/workflows/python.yml
new file mode 100644
index 00000000..067067a6
--- /dev/null
+++ b/.github/workflows/python.yml
@@ -0,0 +1,28 @@
+name: Python Library
+
+on: [push]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ["3.5", "3.6", "3.7", "3.8"]
+    steps:
+    - uses: actions/checkout@v1
+    - name: Set up Python ${{ matrix.python-version }}
+      uses: actions/setup-python@v1
+      with:
+        python-version: ${{ matrix.python-version }}
+    - name: Set up env
+      run: |
+        python -m pip install --upgrade pip
+        pip install tox
+    - name: Lint with flake8
+      run: |
+        tox -e flake
+    - name: Test with pytest
+      run: |
+        # use "py", which is the default python version
+        tox -e py
diff --git a/dev-requirements.txt b/dev-requirements.txt
new file mode 100644
index 00000000..e01a8206
--- /dev/null
+++ b/dev-requirements.txt
@@ -0,0 +1,3 @@
+pytest
+pytest-cov
+pytest-asyncio
diff --git a/optional-requirements.txt b/optional-requirements.txt
index aeaf3994..00cd3324 100644
--- a/optional-requirements.txt
+++ b/optional-requirements.txt
@@ -1,4 +1,4 @@
 cryptg
 pysocks
-hachoir3
+hachoir
 pillow
diff --git a/readthedocs/developing/testing.rst b/readthedocs/developing/testing.rst
new file mode 100644
index 00000000..badb7dc6
--- /dev/null
+++ b/readthedocs/developing/testing.rst
@@ -0,0 +1,87 @@
+=====
+Tests
+=====
+
+Telethon uses `Pytest <https://pytest.org/>`__, for testing, `Tox
+<https://tox.readthedocs.io/en/latest/>`__ for environment setup, and
+`pytest-asyncio <https://pypi.org/project/pytest-asyncio/>`__ and `pytest-cov
+<https://pytest-cov.readthedocs.io/en/latest/>`__ for asyncio and 
+`coverage <https://coverage.readthedocs.io/>`__ integration.
+
+While reading the full documentation for these is probably a good idea, there
+is a lot to read, so a brief summary of these tools is provided below for
+convienience.
+
+Brief Introduction to Pytest
+============================
+
+`Pytest <https://pytest.org/>`__ is a tool for discovering and running python
+tests, as well as allowing modular reuse of test setup code using fixtures.
+
+Most Pytest tests will look something like this::
+
+    from module import my_thing, my_other_thing
+
+    def test_my_thing(fixture):
+        assert my_thing(fixture) == 42
+
+    @pytest.mark.asyncio
+    async def test_my_thing(event_loop):
+        assert await my_other_thing(loop=event_loop) == 42
+
+Note here:
+
+ 1. The test imports one specific function. The role of unit tests is to test
+    that the implementation of some unit, like a function or class, works.
+    It's role is not so much to test that components interact well with each
+    other. I/O, such as connecting to remote servers, should be avoided. This
+    helps with quickly identifying the source of an error, finding silent
+    breakage, and makes it easier to cover all possible code paths.
+
+    System or integration tests can also be useful, but are currently out of
+    scope of Telethon's automated testing.
+
+ 2. A function ``test_my_thing`` is declared. Pytest searches for files
+    starting with ``test_``, classes starting with ``Test`` and executes any
+    functions or methods starting with ``test_`` it finds.
+
+ 3. The function is declared with a parameter ``fixture``. Fixtures are used to
+    request things required to run the test, such as temporary directories,
+    free TCP ports, Connections, etc. Fixtures are declared by simply adding
+    the fixture name as parameter. A full list of available fixtures can be
+    found with the ``pytest --fixtures`` command.
+
+ 4. The test uses a simple ``assert`` to test some condition is valid.  Pytest
+    uses some magic to ensure that the errors from this are readable and easy
+    to debug.
+
+ 5. The ``pytest.mark.asyncio`` fixture is provided by ``pytest-asyncio``. It
+    starts a loop and executes a test function as coroutine. This should be
+    used for testing asyncio code. It also declares the ``event_loop``
+    fixture, which will request an ``asyncio`` event loop.
+
+Brief Introduction to Tox
+=========================
+
+`Tox <https://tox.readthedocs.io/en/latest/>`__ is a tool for automated setup
+of virtual environments for testing. While the tests can be run directly by
+just running ``pytest``, this only tests one specific python version in your
+existing environment, which will not catch e.g. undeclared dependencies, or
+version incompatabilities.
+
+Tox environments are declared in the ``tox.ini`` file. The default
+environments, declared at the top, can be simply run with ``tox``. The option
+``tox -e py36,flake`` can be used to request specific environments to be run.
+
+Brief Introduction to Pytest-cov
+================================
+
+Coverage is a useful metric for testing. It measures the lines of code and
+branches that are exercised by the tests. The higher the coverage, the more
+likely it is that any coding errors will be caught by the tests.
+
+A brief coverage report can be generated with the ``--cov`` option to ``tox``,
+which will be passed on to ``pytest``. Additionally, the very useful HTML
+report can be generated with ``--cov --cov-report=html``, which contains a
+browsable copy of the source code, annotated with coverage information for each
+line.
diff --git a/readthedocs/index.rst b/readthedocs/index.rst
index 9f28deda..0776e3f2 100644
--- a/readthedocs/index.rst
+++ b/readthedocs/index.rst
@@ -93,6 +93,7 @@ You can also use the menu on the left to quickly skip over sections.
     developing/test-servers.rst
     developing/project-structure.rst
     developing/coding-style.rst
+    developing/testing.rst
     developing/understanding-the-type-language.rst
     developing/tips-for-porting-the-project.rst
     developing/telegram-api-in-other-languages.rst
diff --git a/telethon/client/telegrambaseclient.py b/telethon/client/telegrambaseclient.py
index b5c9aec0..162835ea 100644
--- a/telethon/client/telegrambaseclient.py
+++ b/telethon/client/telegrambaseclient.py
@@ -662,7 +662,7 @@ class TelegramBaseClient(abc.ABC):
             self._exported_sessions[cdn_redirect.dc_id] = session
 
         self._log[__name__].info('Creating new CDN client')
-        client = TelegramBareClient(
+        client = TelegramBaseClient(
             session, self.api_id, self.api_hash,
             proxy=self._sender.connection.conn.proxy,
             timeout=self._sender.connection.get_timeout()
diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/tests/telethon/__init__.py b/tests/telethon/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/tests/telethon/crypto/test_rsa.py b/tests/telethon/crypto/test_rsa.py
new file mode 100644
index 00000000..a1a949d2
--- /dev/null
+++ b/tests/telethon/crypto/test_rsa.py
@@ -0,0 +1,37 @@
+"""
+tests for telethon.crypto.rsa
+"""
+import pytest
+
+from telethon.crypto import rsa
+
+@pytest.fixture
+def server_key_fp():
+    """factory to return a key, old if so chosen"""
+    def _server_key_fp(old: bool):
+        for fp, data in rsa._server_keys.items():
+            _, old_key = data
+            if old_key == old:
+                return fp
+
+    return _server_key_fp
+
+def test_encryption_inv_key():
+    """test for #1324"""
+    assert rsa.encrypt("invalid", b"testdata") is None
+
+def test_encryption_old_key(server_key_fp):
+    """test for #1324"""
+    assert rsa.encrypt(server_key_fp(old=True), b"testdata") is None
+
+def test_encryption_allowed_old_key(server_key_fp):
+    data = rsa.encrypt(server_key_fp(old=True), b"testdata", use_old=True)
+    # we can't verify the data is actually valid because we don't have
+    # the decryption keys
+    assert data is not None and len(data) == 256
+
+def test_encryption_current_key(server_key_fp):
+    data = rsa.encrypt(server_key_fp(old=False), b"testdata")
+    # we can't verify the data is actually valid because we don't have
+    # the decryption keys
+    assert data is not None and len(data) == 256
diff --git a/tests/telethon/test_helpers.py b/tests/telethon/test_helpers.py
new file mode 100644
index 00000000..689db8af
--- /dev/null
+++ b/tests/telethon/test_helpers.py
@@ -0,0 +1,59 @@
+"""
+tests for telethon.helpers
+"""
+
+from base64 import b64decode
+
+import pytest
+
+from telethon import helpers
+
+
+def test_strip_text():
+    assert helpers.strip_text(" text ", []) == "text"
+    # I can't interpret the rest of the code well enough yet
+
+
+class TestSyncifyAsyncContext:
+    class NoopContextManager:
+        def __init__(self, loop):
+            self.count = 0
+            self.loop = loop
+
+        async def __aenter__(self):
+            self.count += 1
+            return self
+
+        async def __aexit__(self, exc_type, *args):
+            assert exc_type is None
+            self.count -= 1
+
+        __enter__ = helpers._sync_enter
+        __exit__ = helpers._sync_exit
+
+    def test_sync_acontext(self, event_loop):
+        contm = self.NoopContextManager(event_loop)
+        assert contm.count == 0
+
+        with contm:
+            assert contm.count == 1
+
+        assert contm.count == 0
+
+    @pytest.mark.asyncio
+    async def test_async_acontext(self, event_loop):
+        contm = self.NoopContextManager(event_loop)
+        assert contm.count == 0
+
+        async with contm:
+            assert contm.count == 1
+
+        assert contm.count == 0
+
+
+def test_generate_key_data_from_nonce():
+    gkdfn = helpers.generate_key_data_from_nonce
+
+    key_expect = b64decode(b'NFwRFB8Knw/kAmvPWjtrQauWysHClVfQh0UOAaABqZA=')
+    nonce_expect = b64decode(b'1AgjhU9eDvJRjFik73bjR2zZEATzL/jLu9yodYfWEgA=')
+    assert gkdfn(123456789, 1234567) == (key_expect, nonce_expect)
diff --git a/tox.ini b/tox.ini
new file mode 100644
index 00000000..53f33505
--- /dev/null
+++ b/tox.ini
@@ -0,0 +1,24 @@
+[tox]
+envlist = py35,py36,py37,py38
+
+[testenv]
+deps =
+    -rrequirements.txt
+    -roptional-requirements.txt
+    -rdev-requirements.txt
+commands =
+    # NOTE: you can run any command line tool here - not just tests
+    pytest {posargs}
+
+# run with tox -e flake
+[testenv:flake]
+deps =
+    -rrequirements.txt
+    -roptional-requirements.txt
+    -rdev-requirements.txt
+    flake8
+commands =
+    # stop the build if there are Python syntax errors or undefined names
+    flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
+    # exit-zero treats all errors as warnings. The GitHub editor is 127 chars wide
+    flake8 . --count --exit-zero --exclude telethon/tl/,telethon/errors/rpcerrorlist.py --max-complexity=10 --max-line-length=127 --statistics