diff --git a/libbmc/doi.py b/libbmc/doi.py
index f976489..925231d 100644
--- a/libbmc/doi.py
+++ b/libbmc/doi.py
@@ -10,7 +10,7 @@ from libbmc import tools
 
 # Taken from
 # https://stackoverflow.com/questions/27910/finding-a-doi-in-a-document-or-page/10324802#10324802
-REGEX = re.compile(r"\b(10[.][0-9]{4,}(?:[.][0-9]+)*/(?:(?![\"&\'<>])\S)+)\b",
+REGEX = re.compile(r"\b(10[.][0-9]{4,}(?:[.][0-9]+)*/(?:(?![\"&\'])\S)+)\b",
                    re.IGNORECASE)
 # Base dx.doi.org URL for redirections
 DX_URL = "http://dx.doi.org/{doi}"
@@ -22,6 +22,30 @@ def is_valid(doi):
 
     :param doi: The DOI to be checked.
     :returns: Boolean indicating whether the DOI is valid or not.
+
+    >>> is_valid('10.1209/0295-5075/111/40005')
+    True
+
+    >>> is_valid('10.1016.12.31/nature.S0735-1097(98)2000/12/31/34:7-7')
+    True
+
+    >>> is_valid('10.1002/(SICI)1522-2594(199911)42:5<952::AID-MRM16>3.0.CO;2-S')
+    True
+
+    >>> is_valid('10.1007/978-3-642-28108-2_19')
+    True
+
+    >>> is_valid('10.1007.10/978-3-642-28108-2_19')
+    True
+
+    >>> is_valid('10.1016/S0735-1097(98)00347-7')
+    True
+
+    >>> is_valid('10.1579/0044-7447(2006)35\[89:RDUICP\]2.0.CO;2')
+    True
+
+    >>> is_valid('<geo coords="10.4515260,51.1656910"></geo>')
+    False
     """
     match = REGEX.match(doi)
     return ((match is not None) and (match.group(0) == doi))
@@ -33,6 +57,9 @@ def extract_from_text(text):
 
     :param text: The text to extract DOIs from.
     :returns: A list of found DOIs.
+
+    >>> sorted(extract_from_text('10.1209/0295-5075/111/40005 10.1016.12.31/nature.S0735-1097(98)2000/12/31/34:7-7 10.1002/(SICI)1522-2594(199911)42:5<952::AID-MRM16>3.0.CO;2-S 10.1007/978-3-642-28108-2_19 10.1007.10/978-3-642-28108-2_19 10.1016/S0735-1097(98)00347-7 10.1579/0044-7447(2006)35\[89:RDUICP\]2.0.CO;2 <geo coords="10.4515260,51.1656910"></geo>'))
+    ['10.1002/(SICI)1522-2594(199911)42:5<952::AID-MRM16>3.0.CO;2-S', '10.1007.10/978-3-642-28108-2_19', '10.1007/978-3-642-28108-2_19', '10.1016.12.31/nature.S0735-1097(98)2000/12/31/34:7-7', '10.1016/S0735-1097(98)00347-7', '10.1209/0295-5075/111/40005', '10.1579/0044-7447(2006)35\\\\[89:RDUICP\\\\]2.0.CO;2']
     """
     return tools.remove_duplicates(REGEX.findall(text))
 
@@ -41,8 +68,14 @@ def to_URL(dois):
     """
     Convert a list of canonical DOIs to a list of DOIs URLs.
 
-    :param dois: List of canonical DOIs.
-    :returns: A list of DOIs URLs.
+    :param dois: List of canonical DOIs. Can also be a single canonical DOI.
+    :returns: A list of DOIs URLs (resp. a single value).
+
+    >>> to_URL(['10.1209/0295-5075/111/40005'])
+    ['http://dx.doi.org/10.1209/0295-5075/111/40005']
+
+    >>> to_URL('10.1209/0295-5075/111/40005')
+    'http://dx.doi.org/10.1209/0295-5075/111/40005'
     """
     if isinstance(dois, list):
         return [DX_URL.format(doi=doi) for doi in dois]
@@ -54,13 +87,29 @@ def to_canonical(urls):
     """
     Convert a list of DOIs URLs to a list of canonical DOIs.
 
-    :param dois: A list of DOIs URLs.
-    :returns: List of canonical DOIs.
+    :param dois: A list of DOIs URLs. Can also be a single DOI URL.
+    :returns: List of canonical DOIs (resp. a single value). ``None`` if an \
+            error occurred.
+
+    >>> to_canonical(['http://dx.doi.org/10.1209/0295-5075/111/40005'])
+    ['10.1209/0295-5075/111/40005']
+
+    >>> to_canonical('http://dx.doi.org/10.1209/0295-5075/111/40005')
+    '10.1209/0295-5075/111/40005'
+
+    >>> to_canonical('aaaa') is None
+    True
+
+    >>> to_canonical(['aaaa']) is None
+    True
     """
-    if isinstance(urls, list):
-        return [extract_from_text(url) for url in urls]
-    else:
-        return extract_from_text(urls)
+    try:
+        if isinstance(urls, list):
+            return [extract_from_text(url)[0] for url in urls]
+        else:
+            return extract_from_text(urls)[0]
+    except IndexError:
+        return None
 
 
 def get_oa_version(doi):
@@ -73,6 +122,9 @@ def get_oa_version(doi):
 
     :param doi: A canonical DOI.
     :returns: The URL of the OA version of the given DOI, or ``None``.
+
+    >>> get_oa_version('10.1209/0295-5075/111/40005')
+    'http://arxiv.org/abs/1506.06690'
     """
     # If DOI is a link, truncate it
     try:
@@ -91,6 +143,9 @@ def get_linked_version(doi):
 
     :param doi: A canonical DOI.
     :returns: The canonical URL behind the DOI, or ``None``.
+
+    >>> get_linked_version('10.1209/0295-5075/111/40005')
+    'http://stacks.iop.org/0295-5075/111/i=4/a=40005?key=crossref.9ad851948a976ecdf216d4929b0b6f01'
     """
     try:
         r = requests.head(to_URL(doi))
@@ -109,6 +164,9 @@ def get_bibtex(doi):
 
     :param doi: The canonical DOI to get BibTeX from.
     :returns: A BibTeX string or ``None``.
+
+    >>> get_bibtex('10.1209/0295-5075/111/40005')
+    '@article{Verney_2015,\\n\\tdoi = {10.1209/0295-5075/111/40005},\\n\\turl = {http://dx.doi.org/10.1209/0295-5075/111/40005},\\n\\tyear = 2015,\\n\\tmonth = {aug},\\n\\tpublisher = {{IOP} Publishing},\\n\\tvolume = {111},\\n\\tnumber = {4},\\n\\tpages = {40005},\\n\\tauthor = {Lucas Verney and Lev Pitaevskii and Sandro Stringari},\\n\\ttitle = {Hybridization of first and second sound in a weakly interacting Bose gas},\\n\\tjournal = {{EPL}}\\n}'
     """
     try:
         r = requests.get(to_URL(doi),
diff --git a/libbmc/fetcher.py b/libbmc/fetcher.py
index cd3acca..e6ff516 100644
--- a/libbmc/fetcher.py
+++ b/libbmc/fetcher.py
@@ -25,6 +25,8 @@ def download(url, proxies=[None]):
     :returns: A tuple of the raw content of the downloaded data and its \
             associated content-type. Returns ``(None, None)`` if it was \
             unable to download the document.
+
+    # TODO: Unittests
     """
     # Loop over all available connections
     for proxy in proxies: