             XCTAssertTrue(event.updatedIndices.isEmpty)
             exp.fulfill()
             }
-            .addDisposableTo(disposeBag)
+            .disposed(by: disposeBag)
 
         a.append(contentsOf: ["buzz", "sugar", "tea"].makeIterator())
 
         waitForExpectations(timeout: 1) { (error) in
-            XCTAssertNil(error, "\(error)")
+            XCTAssertNil(error, "\(String(describing: error))")
         }
     }
 

            XCTAssertTrue(event.updatedIndices.isEmpty)
            exp.fulfill()
            }
            .addDisposableTo(disposeBag)

        a.replaceSubrange(1...2, with: ["milk", "coffee", "tea"])

        waitForExpectations(timeout: 1) { (error) in
            XCTAssertNil(error, "\(error)")
        }
    }


                exp.fulfill()
            }
            }
            .disposed(by: disposeBag)

        _ = a.popLast()

        waitForExpectations(timeout: 1) { (error) in
            XCTAssertNil(error, "\(String(describing: error))")
        }

        XCTAssertEqual(2, observed.count)
