Add unit test for 'iso' aliasing errors

tests/errors/cypclass_iso_errors.pyx

+# mode: error
+# tag: cpp, cpp11, pthread
+# cython: experimental_cpp_class_def=True, language_level=2
+
+cdef cypclass A activable:
+    pass
+
+def test_name_aliasing():
+    cdef iso A iso_a
+    iso_a = consume A()
+
+    # Aliasing non-consumed to iso
+    cdef iso A iso_b
+    iso_b = iso_a
+
+    cdef iso A iso_c
+    iso_c = A()
+
+    cdef iso A iso_d
+    iso_d = activate(consume A())
+
+    cdef iso A iso_e
+    iso_e = <object> A()
+
+    # Aliasing iso
+    cdef iso A iso_f
+    iso_f = iso_a
+
+    cdef active A active_a
+    active_a = iso_a
+
+    cdef A ref_a
+    ref_a = iso_a
+
+    cdef object py_a
+    py_a = iso_a
+
+
+cdef cypclass Field:
+    Field foo(self, Field other):
+        return other
+
+cdef cypclass Origin:
+    Field field
+
+    __init__(self):
+        self.field = Field()
+
+    Field bar(self, Field other):
+        return other
+
+def test_field_aliasing():
+    cdef iso Origin o = consume Origin()
+    cdef object py_field
+
+    # OK - can pass consumed arguments
+    o.bar(consume Field()).foo(consume Field())
+
+    # ERR - aliasing field of iso to pyobject
+    py_field = o.field
+
+    # ERR - pyobject to field of iso
+    o.field = py_field
+
+    # ERR - aliasing field of iso
+    field = o.field
+
+    # ERR - consuming field of iso
+    field2 = consume o.field
+
+    # ERR - non_consumed argument
+    o.bar(Field())
+
+    # ERR - aliasing the returned reference
+    c = o.bar(consume Field())
+
+
+_ERRORS = u'''
+14:12: Cannot assign type 'iso A' to 'iso A'
+17:13: Cannot assign type 'A' to 'iso A'
+20:20: Cannot assign type 'active A' to 'iso A'
+23:12: Cannot convert Python object to 'iso A'
+27:12: Cannot assign type 'iso A' to 'iso A'
+30:15: Cannot assign type 'iso A' to 'active A'
+33:12: Cannot assign type 'iso A' to 'A'
+36:11: Cannot convert 'iso A' to Python object
+60:16: Cannot convert 'iso-> Field' to Python object
+63:14: Cannot convert Python object to 'iso-> Field'
+66:13: Cannot assign type 'iso-> Field' to 'iso-> Field'
+72:15: Cannot assign type 'Field' to 'iso-> Field'
+75:13: Cannot assign type 'iso-> Field' to 'iso-> Field'
+'''