Add unit tests for distribute tuple

Author: ChristinaTrinh

test-data/unit/check-tuples.test

@@ -1815,3 +1815,43 @@ class tuple_aa_subclass(Tuple[A, A]): ...
 
 inst_tuple_aa_subclass: tuple_aa_subclass = tuple_aa_subclass((A(), A()))[:]  # E: Incompatible types in assignment (expression has type "Tuple[A, A]", variable has type "tuple_aa_subclass")
 [builtins fixtures/tuple.pyi]
+
+# ----------------------------------------------------------------------------
+# Union-in-Tuple distribution
+# ----------------------------------------------------------------------------
+
+[case testTupleUnionDistributionSuccess]
+from typing import Tuple, Optional, Union
+
+def f1(x: Tuple[float, Optional[float]]) -> Union[Tuple[float, float], Tuple[float, None]]:
+    return x
+
+def f2(x: Tuple[Union[int, str], float]) -> Union[Tuple[int, float], Tuple[str, float]]:
+    return x
+
+def f3(x: Tuple[int, Union[str, None]]) -> Union[Tuple[int, str], Tuple[int, None]]:
+    return x
+
+def f4(x: Tuple[Union[int, float]]) -> Union[Tuple[int], Tuple[float]]:
+    return x
+
+def f5(x: Tuple[Union[int, str], Union[bool, None]]) -> Union[
+    Tuple[int, bool],
+    Tuple[int, None],
+    Tuple[str, bool],
+    Tuple[str, None],
+]:
+    return x
+
+[builtins fixtures/tuple.pyi]
+
+[case testTupleUnionDistributionFail]
+from typing import Tuple, Optional, Union
+
+def g1(x: Tuple[float, Optional[float]]) -> Union[Tuple[float, float], Tuple[str, float]]:
+    return x  # E: Incompatible return value type (got "Tuple[float, Optional[float]]", expected "Union[Tuple[float, float], Tuple[str, float]]")
+
+def g2(x: Tuple[float, Optional[float]]) -> Union[Tuple[float, str], Tuple[float, None]]:
+    return x # E: Incompatible return value type (got "Tuple[float, Optional[float]]", expected "Union[Tuple[float, str], Tuple[float, None]]")
+
+[builtins fixtures/tuple.pyi]