Add unit test

Author: pkch

test-data/unit/check-isinstance.test

@@ -1344,3 +1344,11 @@ def f(x: object) -> None:
     reveal_type(b)  # E: Revealed type is '__main__.A'
 [builtins fixtures/isinstance.pyi]
 [out]
+
+[case testIsInstanceWithTypeVariable]
+from typing import *
+def f(x: Union[int, str], typ: type) -> None:
+    if isinstance(x, (typ, int)):
+        x + 1  # E: Unsupported operand types for + (likely involving Union)
+[builtins fixtures/isinstancelistset.pyi]
+

test-data/unit/fixtures/isinstancelistset.pyi

@@ -0,0 +1,50 @@
+from typing import builtinclass, Iterable, Iterator, Generic, TypeVar, List, Mapping, overload, Tuple, Set, Union
+
+@builtinclass
+class object:
+    def __init__(self) -> None: pass
+
+@builtinclass
+class type:
+    def __init__(self, x) -> None: pass
+
+class tuple: pass
+class function: pass
+
+def isinstance(x: object, t: Union[type, Tuple]) -> bool: pass
+
+@builtinclass
+class int:
+    def __add__(self, x: int) -> int: pass
+@builtinclass
+class bool(int): pass
+@builtinclass
+class str:
+    def __add__(self, x: str) -> str: pass
+    def __getitem__(self, x: int) -> str: pass
+
+T = TypeVar('T')
+KT = TypeVar('KT')
+VT = TypeVar('VT')
+
+class list(Iterable[T], Generic[T]):
+    def __iter__(self) -> Iterator[T]: pass
+    def __mul__(self, x: int) -> list[T]: pass
+    def __setitem__(self, x: int, v: T) -> None: pass
+    def __getitem__(self, x: int) -> T: pass
+    def __add__(self, x: List[T]) -> T: pass
+
+class dict(Iterable[KT], Mapping[KT, VT], Generic[KT, VT]):
+    @overload
+    def __init__(self, **kwargs: VT) -> None: pass
+    @overload
+    def __init__(self, arg: Iterable[Tuple[KT, VT]], **kwargs: VT) -> None: pass
+    def __setitem__(self, k: KT, v: VT) -> None: pass
+    def __iter__(self) -> Iterator[KT]: pass
+    def update(self, a: Mapping[KT, VT]) -> None: pass
+
+class set(Iterable[T], Generic[T]):
+    def __iter__(self) -> Iterator[T]: pass
+    def add(self, x: T) -> None: pass
+    def discard(self, x: T) -> None: pass
+    def update(self, x: Set[T]) -> None: pass