Add a test to fine-grained

Author: sobolevn

test-data/unit/fine-grained.test

@@ -3705,6 +3705,34 @@ def foo() -> None:
 ==
 b.py:4: error: Incompatible types in assignment (expression has type "str", variable has type "int")
 
+[case testTypedDictUpdateReadOnly]
+import b
+[file a.py]
+from typing_extensions import TypedDict, ReadOnly
+Point = TypedDict('Point', {'x': int, 'y': int})
+p = Point(x=1, y=2)
+[file a.py.2]
+from typing_extensions import TypedDict, ReadOnly
+class Point(TypedDict):
+    x: int
+    y: ReadOnly[int]
+p = Point(x=1, y=2)
+[file a.py.3]
+from typing_extensions import TypedDict, ReadOnly
+Point = TypedDict('Point', {'x': ReadOnly[int], 'y': int})
+p = Point(x=1, y=2)
+[file b.py]
+from a import Point
+def foo(x: Point) -> None:
+    x['x'] = 1
+    x['y'] = 2
+[builtins fixtures/dict.pyi]
+[out]
+==
+b.py:4: error: ReadOnly TypedDict key "y" TypedDict is mutated
+==
+b.py:3: error: ReadOnly TypedDict key "x" TypedDict is mutated
+
 [case testBasicAliasUpdate]
 import b
 [file a.py]