Add support for pydantic dataclasses (#406)

tests/inputs/bool/test_bool.py

@@ -1,6 +1,19 @@
+import pytest
+
 from tests.output_betterproto.bool import Test
+from tests.output_betterproto_pydantic.bool import Test as TestPyd
 
 
 def test_value():
     message = Test()
     assert not message.value, "Boolean is False by default"
+
+
+def test_pydantic_no_value():
+    with pytest.raises(ValueError):
+        TestPyd()
+
+
+def test_pydantic_value():
+    message = Test(value=False)
+    assert not message.value