[Runtime] Add test for casting an Error type to NSObject

Author: DougGregor

test/stdlib/ErrorBridged.swift

@@ -767,4 +767,29 @@ ErrorBridgingTests.test("@objc error domains for nested types") {
               String(reflecting: NonPrintAsObjCError.self))
 }
 
+@inline(never)
+@_optimize(none)
+func anyToAny<T, U>(_ a: T, _ : U.Type) -> U {
+  return a as! U
+}
+
+ErrorBridgingTests.test("error-to-NSObject casts") {
+  let error = MyCustomizedError(code: 12345)
+
+  // Unconditional cast
+  let nsErrorAsObject1 = unconditionalCast(error, to: NSObject.self)
+  let nsError1 = unconditionalCast(nsErrorAsObject1, to: NSError.self)
+  expectEqual("custom", nsError1.domain)
+  expectEqual(12345, nsError1.code)
+
+  // Conditional cast
+  let nsErrorAsObject2 = conditionalCast(error, to: NSObject.self)!
+  let nsError2 = unconditionalCast(nsErrorAsObject2, to: NSError.self)
+  expectEqual("custom", nsError2.domain)
+  expectEqual(12345, nsError2.code)
+
+  // "is" check
+  expectTrue(error is NSObject)
+}
+
 runAllTests()