Assert.css, closes #43

attest/__init__.py

@@ -868,6 +868,24 @@ def json(self):
             import json
         return Assert(json.loads(self.obj))
 
+    def css(self, selector):
+        """Parse the wrapped object as
+        :abbr:`HTML (HyperText Markup Language)` and return a list (wrapped
+        in :class:`Assert`) of elements matching the
+        :abbr:`CSS (Cascading Style Sheets)` *selector*.  Requires lxml 2.0
+        or newer.
+
+        .. note::
+
+            Not tested on Python 2.5 and PyPy due to difficulties
+            installing lxml on these implementations.
+
+        .. versionadded:: 0.4
+
+        """
+        from lxml import html
+        return Assert(html.fromstring(self.obj).cssselect(selector))
+
     def __repr__(self):
         """Not proxied to the wrapped object. To test that do something
         like::

attest/tests/asserts.py

@@ -251,3 +251,26 @@ def json():
 
     with Assert.raises(AssertionError):
         Assert('{"works": true}').json == dict(works=False)
+
+
+try:
+    import lxml
+except ImportError:
+    lxml = None
+
+@suite.test_if(lxml)
+def css():
+    """Assert.css"""
+
+    html = Assert("""
+        <div id="maincontent">
+            <div class="container">
+                <p>Hello World</p>
+            </div>
+        </div>
+    """)
+
+    html.css('#maincontent .container p')[0].text == 'Hello World'
+
+    with Assert.raises(AssertionError):
+        html.css('#maincontent .container p')[0].text != 'Hello World'

docs/api.rst

@@ -39,7 +39,8 @@ Asserting conditions
 --------------------
 
 .. autoclass:: Assert
-   :members: isinstance, not_isinstance, issubclass, not_issubclass, json,
+   :members:
+       isinstance, not_isinstance, issubclass, not_issubclass, json, css,
        __str__, __getattr__, __call__, __getitem__, __eq__, __ne__, is_,
        is_not, __contains__, in_, not_in, __lt__, __le__, __gt__, __ge__,
        __nonzero__, __repr__

tox.ini

@@ -2,6 +2,7 @@
 envlist = py25, py26, py27, py31, pypy, docs
 
 [testenv]
+deps = lxml>=2.0
 commands = python runtests.py
 
 [testenv:py25]