From 827388b4fef0e7f466f96882d3aaed1cd85cfc2f Mon Sep 17 00:00:00 2001
From: John Carter <john@therefromhere.org>
Date: Mon, 1 Jun 2020 01:51:50 +1200
Subject: [PATCH] Add a test assertion that `default_factory` can return a
 singleton (#1523)

---
 changes/1523-therefromhere.md |  1 +
 tests/test_dataclasses.py     | 17 +++++++++++++++++
 tests/test_main.py            | 14 ++++++++++++++
 3 files changed, 32 insertions(+)
 create mode 100644 changes/1523-therefromhere.md

diff --git a/changes/1523-therefromhere.md b/changes/1523-therefromhere.md
new file mode 100644
index 0000000000..3a8256776a
--- /dev/null
+++ b/changes/1523-therefromhere.md
@@ -0,0 +1 @@
+Add a test assertion that `default_factory` can return a singleton
diff --git a/tests/test_dataclasses.py b/tests/test_dataclasses.py
index 22b126a136..d799e35a0c 100644
--- a/tests/test_dataclasses.py
+++ b/tests/test_dataclasses.py
@@ -431,6 +431,23 @@ class User:
     assert fields['aliases'].default == {'John': 'Joey'}
 
 
+def test_default_factory_singleton_field():
+    class MySingleton:
+        pass
+
+    class MyConfig:
+        arbitrary_types_allowed = True
+
+    MY_SINGLETON = MySingleton()
+
+    @pydantic.dataclasses.dataclass(config=MyConfig)
+    class Foo:
+        singleton: MySingleton = dataclasses.field(default_factory=lambda: MY_SINGLETON)
+
+    # Returning a singleton from a default_factory is supported
+    assert Foo().singleton is Foo().singleton
+
+
 def test_schema():
     @pydantic.dataclasses.dataclass
     class User:
diff --git a/tests/test_main.py b/tests/test_main.py
index 76e05b70ad..c70ada964e 100644
--- a/tests/test_main.py
+++ b/tests/test_main.py
@@ -1087,6 +1087,20 @@ class FunctionModel(BaseModel):
     m = FunctionModel()
     assert m.uid is uuid4
 
+    # Returning a singleton from a default_factory is supported
+    class MySingleton:
+        pass
+
+    MY_SINGLETON = MySingleton()
+
+    class SingletonFieldModel(BaseModel):
+        singleton: MySingleton = Field(default_factory=lambda: MY_SINGLETON)
+
+        class Config:
+            arbitrary_types_allowed = True
+
+    assert SingletonFieldModel().singleton is SingletonFieldModel().singleton
+
 
 @pytest.mark.skipif(sys.version_info < (3, 7), reason='field constraints are set but not enforced with python 3.6')
 def test_none_min_max_items():