Add unit test for 'active' aliasing errors

tests/errors/cypclass_active_errors.pyx

+# mode: error
+# tag: cpp, cpp11, pthread
+# cython: experimental_cpp_class_def=True, language_level=2
+
+cdef cypclass A activable:
+    void f(self, A other):
+        pass
+
+    void f_iso(self, iso A other):
+        pass
+
+    void f_locked(self, locked A other):
+        pass
+
+    void f_active(self, active A other):
+        pass
+
+
+def test_aliasing():
+    cdef active A active_a
+
+    cdef iso A iso_a
+    iso_a = active_a
+
+    cdef locked A locked_a
+    locked_a = active_a
+
+    cdef A ref_a
+    ref_a = active_a
+
+def test_calling():
+    a = activate(consume A())
+
+    a.f(NULL, A())
+
+    a.f(NULL, consume A())
+
+    cdef iso A iso_a
+    a.f_iso(NULL, consume iso_a)
+
+    cdef locked A locked_a
+    a.f_locked(NULL, locked_a)
+
+    cdef active A active_a
+    a.f_active(NULL, active_a)
+
+
+_ERRORS = u'''
+23:12: Cannot assign type 'active A' to 'iso A'
+26:15: Cannot assign type 'active A' to 'locked A'
+29:12: Cannot assign type 'active A' to 'A'
+34:15: Cannot assign type 'A' to 'iso-> A'
+'''