     let expected = [1, 2, 3]
     var actual = [Int]()
     let sequence = source.async.removeDuplicates() { prev, next in
-      if next < 0 {
-        throw NSError(domain: NSCocoaErrorDomain, code: -1, userInfo: nil)
-      }
+      let next = try throwOn(-1, next)
       return prev == next
     }
 

//
// This source file is part of the Swift Async Algorithms open source project
//
// Copyright (c) 2021 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information

      }
      XCTFail()
    } catch {
      XCTAssertEqual(Failure(), error as? Failure)
    }
    XCTAssertEqual(actual, expected)
  }
