Fix bug in exception handling for which(). Also standardize exceptions

to always be ValueError. Add the beginnings of to_dict()

test/test_struct.py

@@ -0,0 +1,64 @@
+import pytest
+import capnp
+import os
+
+this_dir = os.path.dirname(__file__)
+
+@pytest.fixture
+def addressbook():
+     return capnp.load(os.path.join(this_dir, 'addressbook.capnp'))
+
+def test_which_builder(addressbook):
+    addresses = addressbook.AddressBook.new_message()
+    people = addresses.init('people', 2)
+
+    alice = people[0]
+    alice.employment.school = "MIT"
+
+    assert alice.employment.which() == "school"
+
+    bob = people[1]
+
+    assert bob.employment.which() == "unemployed"
+    
+    bob.employment.unemployed = None
+
+    assert bob.employment.which() == "unemployed"
+
+def test_which_reader(addressbook):
+    def writeAddressBook(fd):
+        message = capnp._MallocMessageBuilder()
+        addressBook = message.init_root(addressbook.AddressBook)
+        people = addressBook.init('people', 2)
+
+        alice = people[0]
+        alice.employment.school = "MIT"
+
+        bob = people[1]
+        bob.employment.unemployed = None
+
+        capnp._write_packed_message_to_fd(fd, message)
+
+    f = open('example', 'w')
+    writeAddressBook(f.fileno())
+    f = open('example', 'r')
+
+    addresses = addressbook.AddressBook.read_packed(f)
+
+    people = addresses.people
+
+    alice = people[0]
+    assert alice.employment.which() == "school"
+
+    bob = people[1]
+    assert bob.employment.which() == "unemployed"
+
+def test_builder_set(addressbook):
+    person = addressbook.Person.new_message()
+
+    person.name = 'test'
+
+    assert person.name == 'test'
+
+    with pytest.raises(ValueError):
+        person.foo = 'test'