Allow passing compiler flags to tox runs

README.rst

@@ -117,6 +117,22 @@ Run ``pytest``:
 
 The network blocking feature supports ``socket``-based transports and ``pycurl``.
 
+Contributing
+------------
+
+To run the tests:
+
+.. code:: bash
+
+    $ tox -p all
+
+If you have troubles with installing ``pycurl`` with ``tox``, you could try to pass ``CPPFLAGS`` and ``LDFLAGS``
+with the ``tox`` command:
+
+.. code:: bash
+
+    $  CPPFLAGS="-I/usr/local/opt/openssl/include" LDFLAGS="-L/usr/local/opt/openssl/lib" tox -p all
+
 Python support
 --------------
 

tox.ini

@@ -4,6 +4,9 @@ envlist = black,pylint,py{27,35,36,37,38,py,py3},no_pycurl,coverage-report
 [testenv]
 setenv =
     PYCURL_SSL_LIBRARY = {env:PYCURL_SSL_LIBRARY:openssl}
+passenv =
+    LDFLAGS
+    CPPFLAGS
 deps =
     coverage
     pytest>=3.0