pypyPackages.mock: Unbreak PyPy for Python 2.7.

Unbreaks many PyPy packages.

pkgs/development/python-modules/mock/default.nix

@@ -20,6 +20,12 @@ buildPythonPackage rec {
   buildInputs = [ unittest2 ];
   propagatedBuildInputs = [ funcsigs six pbr ];
 
+  # On PyPy for Python 2.7 in particular, Mock's tests have a known failure.
+  # Mock upstream has a decoration to disable the failing test and make
+  # everything pass, but it is not yet released. The commit:
+  # https://github.com/testing-cabal/mock/commit/73bfd51b7185#diff-354f30a63fb0907d4ad57269548329e3L12
+  doCheck = !(python.isPyPy && python.isPy27);
+
   checkPhase = ''
     ${python.interpreter} -m unittest discover
   '';