diff --git a/.coveragerc b/.coveragerc
new file mode 100644
index 0000000..2301243
--- /dev/null
+++ b/.coveragerc
@@ -0,0 +1,3 @@
+[report]
+omit =
+    */tests/*
diff --git a/.travis.yml b/.travis.yml
index a4c4ae5..8511f0b 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -4,8 +4,9 @@ dist: bionic
 
 # https://devguide.python.org/#branchstatus
 python:
-  - "3.6"
-  - "3.7"
+  - 3.6
+  - 3.7
+  - 3.8
 
 addons:
   apt:
@@ -13,18 +14,18 @@ addons:
       - libgnutls28-dev
 
 install:
-  - pip install flake8 coverage
+  - pip install flake8 coverage coveralls
   - python setup.py install
 
 script:
   - flake8 sentinel5dl
   - coverage run --source=sentinel5dl -m tests
-  - coverage report
 
 after_success:
   - pip install sphinx sphinx-rtd-theme
   - make -C docs clean html
   - touch docs/build/html/.nojekyll # create this file to prevent Github's Jekyll processing
+  - coveralls
 
 deploy:
   provider: pages
diff --git a/README.rst b/README.rst
index a5aed3e..47748ce 100644
--- a/README.rst
+++ b/README.rst
@@ -3,6 +3,10 @@ Sentinel-5P Downloader
 
 .. image:: https://travis-ci.com/emissions-api/sentinel5dl.svg?branch=master
     :target: https://travis-ci.com/emissions-api/sentinel5dl
+    :alt: CI Builds
+.. image:: https://coveralls.io/repos/github/emissions-api/sentinel5dl/badge.svg?branch=master
+    :target: https://coveralls.io/github/emissions-api/sentinel5dl?branch=master
+    :alt: Test Coverage
 .. image:: https://img.shields.io/github/issues-raw/emissions-api/sentinel5dl?color=blue
     :target: https://github.com/emissions-api/sentinel5dl/issues
     :alt: GitHub issues
diff --git a/docs/Makefile b/docs/Makefile
index d0c3cbf..a4de0bf 100644
--- a/docs/Makefile
+++ b/docs/Makefile
@@ -3,7 +3,7 @@
 
 # You can set these variables from the command line, and also
 # from the environment for the first two.
-SPHINXOPTS    ?=
+SPHINXOPTS    ?= -W
 SPHINXBUILD   ?= sphinx-build
 SOURCEDIR     = source
 BUILDDIR      = build
diff --git a/docs/source/index.rst b/docs/source/index.rst
index 7d41c3d..5ead6ed 100644
--- a/docs/source/index.rst
+++ b/docs/source/index.rst
@@ -1,4 +1,4 @@
-.. include:: ../../readme.rst
+.. include:: ../../README.rst
 
 
 .. toctree::
diff --git a/sentinel5dl/__init__.py b/sentinel5dl/__init__.py
index 278956d..0be61eb 100644
--- a/sentinel5dl/__init__.py
+++ b/sentinel5dl/__init__.py
@@ -38,6 +38,28 @@ def __md5(filename):
     return hash_md5.hexdigest().upper()
 
 
+def __check_md5(filename, base_path):
+    '''Check the md5 sum of a given file against the ESA API.
+
+    :param filename: Path of local file to check
+    :param base_path: Base API path to for this product
+    :returns: If the local file matches the md5 checksum
+    :rtype: bool
+    '''
+    md5file = f'{filename}.md5sum'
+    try:
+        with open(md5file, 'r') as f:
+            md5sum = f.read()
+    except FileNotFoundError:
+        md5sum = __http_request(f'{base_path}/Checksum/Value/$value')
+        md5sum = md5sum.decode('ascii')
+        with open(md5file, 'w') as f:
+            f.write(md5sum)
+
+    # Compare md5 sum
+    return __md5(filename) == md5sum
+
+
 def __http_request(path, filename=None):
     '''Make an HTTP request to the API via HTTP, optionally downloading the
     response.
@@ -140,20 +162,15 @@ def download(products, output_dir='.'):
         uuid = product['uuid']
         filename = os.path.join(output_dir, product['identifier'] + '.nc')
         logger.info(f'Downloading {uuid} to {filename}')
-        path = f'/odata/v1/Products(\'{uuid}\')/$value'
+        base_path = f"/odata/v1/Products('{uuid}')"
 
         # Check if file exist
         if os.path.exists(filename):
-            # Get md5 sum
-            md5um_path = f"/odata/v1/Products('{uuid}')/Checksum/Value/$value"
-            md5sum = __http_request(md5um_path)
-            md5sum = md5sum.decode()
-
-            # Compare md5 sum
-            if __md5(filename) == md5sum:
+            # Skip download if checksum matches
+            if __check_md5(filename, base_path):
                 logger.info(f'Skipping {filename} since it already exist.')
                 continue
             logger.info(f'Overriding {filename} since md5 hash differs.')
 
         # Download file
-        __http_request(path, filename)
+        __http_request(f'{base_path}/$value', filename)
diff --git a/setup.py b/setup.py
index 9bfe958..1e7a6c5 100644
--- a/setup.py
+++ b/setup.py
@@ -11,7 +11,7 @@ def read(filename):
 
 setup(
     name='sentinel5dl',
-    version='0.4',
+    version='0.5',
     description='Sentinel-5p Downloader',
     author='Emissions API Developers',
     license='MIT',
@@ -24,6 +24,7 @@ setup(
         'Programming Language :: Python :: 3',
         'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',
+        'Programming Language :: Python :: 3.8',
         'Operating System :: OS Independent',
         'Topic :: Scientific/Engineering :: GIS',
     ],

diff --git a/tests/__main__.py b/tests/__main__.py
index a3472df..ad1d698 100644
--- a/tests/__main__.py
+++ b/tests/__main__.py
@@ -12,18 +12,22 @@ class TestSentinel5dl(unittest.TestCase):
     def _mock_http_request(self, path, filename=None):
         '''Mock HTTP requests to the ESA API
         '''
+        # download
         if filename is not None:
             self._count_download += 1
             with open(filename, 'wb') as f:
                 f.write(b'123')
             return
 
-        # no nownload
-        self._count_request += 1
+        # search request
         if path.startswith('/api/stub/products?'):
+            self._count_search_request += 1
             with open(os.path.join(testpath, 'products.json'), 'rb') as f:
                 return f.read()
+
+        # checksum request
         if path.endswith('/Checksum/Value/$value'):
+            self._count_checksum_request += 1
             # MD5 checksum for string `123`
             return b'202CB962AC59075B964B07152D234B70'
 
@@ -32,7 +36,8 @@ class TestSentinel5dl(unittest.TestCase):
         make any HTTP requests and reset the request counters.
         '''
         setattr(sentinel5dl, '__http_request', self._mock_http_request)
-        self._count_request = 0
+        self._count_search_request = 0
+        self._count_checksum_request = 0
         self._count_download = 0
 
     def test(self):
@@ -46,7 +51,7 @@ class TestSentinel5dl(unittest.TestCase):
 
         # The result returned by the mock contains four products but claims a
         # total of eight products, making sentinel5dl request resources twice.
-        self.assertEqual(self._count_request, 2)
+        self.assertEqual(self._count_search_request, 2)
         self.assertEqual(result['totalresults'], 8)
         self.assertEqual(result['totalresults'], len(result['products']))
 
@@ -66,10 +71,12 @@ class TestSentinel5dl(unittest.TestCase):
                 with open(filename, 'rb') as f:
                     self.assertEqual(f.read(), b'123')
 
-        # We should have made an additional five requests for checksums:
-        # - one for the file we created manually
-        # - four for the duplicated entries in the loaded test data
-        self.assertEqual(self._count_request, 7)
+            # We should have downloaded four files and have an additional four
+            # files storing md5 checksums
+            self.assertEqual(len(os.listdir(tmpdir)), 8)
+
+        # We should have four checksum requests. One for each file
+        self.assertEqual(self._count_checksum_request, 4)
         # We should have downloaded four unique files
         self.assertEqual(self._count_download, 4)
 

Store also hash files 
We should store the hash files after we have downloaded them. So we can check if the hash file matches the downloaded .nc file without any network connection. This is pretty handy, since the ESA website is painfully slow even for the hash files.
tests/__main__.py::TestSentinel5dl::test