Add any .egg-link paths from VIRTUAL_ENV to sys.path

Adding test_get_sys_path required factoring out
`_get_venv_sitepackages`, because `sys.version_info` cannot be mocked
apparently.

test/test_evaluate/test_sys_path.py

@@ -1,3 +1,5 @@
+import os
+
 from jedi._compatibility import unicode
 from jedi.parser import Parser, load_grammar
 from jedi.evaluate import sys_path, Evaluator
@@ -15,3 +17,15 @@ def test_paths_from_assignment():
 
     # Fail for complicated examples.
     assert paths('sys.path, other = ["a"], 2') == []
+
+
+def test_get_sys_path(monkeypatch):
+    monkeypatch.setenv('VIRTUAL_ENV', os.path.join(os.path.dirname(__file__),
+                                                   'egg-link', 'venv'))
+    def sitepackages_dir(venv):
+        return os.path.join(venv, 'lib', 'python3.4', 'site-packages')
+
+    monkeypatch.setattr('jedi.evaluate.sys_path._get_venv_sitepackages',
+                        sitepackages_dir)
+
+    assert '/path/from/egg-link' in sys_path.get_sys_path()