added test for #19605

Author: randolf-scholz

test-data/unit/check-literal.test

@@ -3135,3 +3135,26 @@ reveal_type(CONST)  # N: Revealed type is "Literal['const']?"
 reveal_type(join(Foo.A, CONST))  # N: Revealed type is "builtins.str"
 reveal_type(join(CONST, Foo.A))  # N: Revealed type is "builtins.str"
 [builtins fixtures/tuple.pyi]
+
+
+[case testLiteralRedundantCast]
+# https://github.com/python/mypy/issues/19055
+# flags: --warn-redundant-cast
+
+from typing import Literal, cast
+
+# "a" is an AnyOf[str, Literal["a"]], denoted Literal['a']?
+# See: https://github.com/python/typing/issues/566
+
+# This cast is not redundant because Literal["a"]? is not identical to Literal["a"]
+LiteralOnly = Literal["a"]
+reveal_type("a")  # N: Revealed type is "Literal['a']?"
+cast(LiteralOnly, "a")
+
+# This cast is redundant because the type is already Literal["a"]
+already_literal: Literal["a"] = "a"
+reveal_type(already_literal)  # N: Revealed type is "Literal['a']"
+cast(LiteralOnly, already_literal)  # E: Redundant cast to "Literal['a']"
+
+LiteralUnion = Literal["a", "b"]
+cast(LiteralUnion, "a")