Make tests fail if an optional dependecy is missing

If lxml or the speedups are missing, the relevant tests are skipped.
(No need to show hundreds of failures.)

This adds one test for each optional dependecy, so that the
suite fails if something is missing, unless a specific enviroment
variable is set. (For when this is expected, like on PyPy.)

tinycss/tests/test_selectors3.py

@@ -9,15 +9,16 @@
 
 
 from __future__ import unicode_literals
+import os
 
 import pytest
-
-from tinycss.core import CoreParser
 try:
     import lxml.cssselect
 except ImportError:
     lxml = None
-else:
+
+from tinycss.core import CoreParser
+if lxml is not None:
     from tinycss.selectors3 import (
         Selector, InvalidSelectorError, Selectors3ParserMixin,
         parse_selector_string, parse_selector_group_string)
@@ -26,6 +27,14 @@ class CSSParser(Selectors3ParserMixin, CoreParser):
         """Custom CSS parser."""
 
 
+def test_lxml():
+    if not os.environ.get('TINYCSS_SKIP_LXML_TESTS'):
+        assert lxml is not None, (
+            'lxml is not not installed, related tests will be skipped. '
+            'Set the TINYCSS_SKIP_LXML_TESTS environment variable '
+            'if this is expected (eg. on PyPy).')
+
+
 @pytest.mark.parametrize(('css_source', 'expected_num_selectors',
                           'expected_errors'), [
     ('', [], []),

tinycss/tests/test_tokenizer.py

@@ -9,12 +9,22 @@
 
 
 from __future__ import unicode_literals
+import os
+
 import pytest
 
 from tinycss.tokenizer import (
     python_tokenize_flat, cython_tokenize_flat, regroup)
 
 
+def test_speedups():
+    if not os.environ.get('TINYCSS_SKIP_SPEEDUPS_TESTS'):
+        assert cython_tokenize_flat is not None, (
+            'Cython speedups are not installed, related tests will '
+            'be skipped. Set the TINYCSS_SKIP_SPEEDUPS_TESTS environment '
+            'variable if this is expected (eg. on PyPy).')
+
+
 @pytest.mark.parametrize(('tokenize', 'css_source', 'expected_tokens'), [
   (tokenize,) + test_data
   for tokenize in (python_tokenize_flat, cython_tokenize_flat)

tox.ini

@@ -5,8 +5,11 @@ envlist = py26,py27,py31,py32,pypy
 deps=
     pytest
     lxml
-changedir={toxworkdir}/logs
-commands=py.test --pyargs tinycss []
+changedir = {toxworkdir}/logs
+commands = py.test --pyargs tinycss []
 
 [testenv:pypy]
-deps=pytest
+deps = pytest
+setenv =
+    TINYCSS_SKIP_SPEEDUPS_TESTS=1
+    TINYCSS_SKIP_LXML_TESTS=1