added testTernaryOperatorWithDefault

Author: randolf-scholz

test-data/unit/check-expressions.test

@@ -2492,3 +2492,21 @@ x + T  # E: Unsupported left operand type for + ("int")
 T()  # E: "TypeVar" not callable
 [builtins fixtures/tuple.pyi]
 [typing fixtures/typing-full.pyi]
+
+[case testTernaryOperatorWithDefault]
+# flags: --python-version 3.13
+# gh-18817
+
+class Ok[T, E = None]:
+    def __init__(self, value: T) -> None:
+        self._value = value
+
+class Err[E, T = None]:
+    def __init__(self, value: E) -> None:
+        self._value = value
+
+type Result[T, E] = Ok[T, E] | Err[E, T]
+
+class Bar[U]:
+    def foo(data: U, cond: bool) -> Result[U, str]:
+        return Ok(data) if cond else Err("Error")