Implementing pickle methods (#535)

Continuing work from #484 by @kevinaud to fix #419

* Implementing pickle methods
* Implement __copy__, __reduce__, and fix __setstate__
* Moved pickling tests into their own file
* Add test for caching

tests/test_features.py

@@ -545,47 +545,6 @@ def test_oneof_default_value_set_causes_writes_wire():
     )
 
 
-def test_recursive_message():
-    from tests.output_betterproto.recursivemessage import Test as RecursiveMessage
-
-    msg = RecursiveMessage()
-
-    assert msg.child == RecursiveMessage()
-
-    # Lazily-created zero-value children must not affect equality.
-    assert msg == RecursiveMessage()
-
-    # Lazily-created zero-value children must not affect serialization.
-    assert bytes(msg) == b""
-
-
-def test_recursive_message_defaults():
-    from tests.output_betterproto.recursivemessage import (
-        Intermediate,
-        Test as RecursiveMessage,
-    )
-
-    msg = RecursiveMessage(name="bob", intermediate=Intermediate(42))
-
-    # set values are as expected
-    assert msg == RecursiveMessage(name="bob", intermediate=Intermediate(42))
-
-    # lazy initialized works modifies the message
-    assert msg != RecursiveMessage(
-        name="bob", intermediate=Intermediate(42), child=RecursiveMessage(name="jude")
-    )
-    msg.child.child.name = "jude"
-    assert msg == RecursiveMessage(
-        name="bob",
-        intermediate=Intermediate(42),
-        child=RecursiveMessage(child=RecursiveMessage(name="jude")),
-    )
-
-    # lazily initialization recurses as needed
-    assert msg.child.child.child.child.child.child.child == RecursiveMessage()
-    assert msg.intermediate.child.intermediate == Intermediate()
-
-
 def test_message_repr():
     from tests.output_betterproto.recursivemessage import Test
 
@@ -699,25 +658,6 @@ def test_service_argument__expected_parameter():
     assert do_thing_request_parameter.annotation == "DoThingRequest"
 
 
-def test_copyability():
-    @dataclass
-    class Spam(betterproto.Message):
-        foo: bool = betterproto.bool_field(1)
-        bar: int = betterproto.int32_field(2)
-        baz: List[str] = betterproto.string_field(3)
-
-    spam = Spam(bar=12, baz=["hello"])
-    copied = copy(spam)
-    assert spam == copied
-    assert spam is not copied
-    assert spam.baz is copied.baz
-
-    deepcopied = deepcopy(spam)
-    assert spam == deepcopied
-    assert spam is not deepcopied
-    assert spam.baz is not deepcopied.baz
-
-
 def test_is_set():
     @dataclass
     class Spam(betterproto.Message):