         }
       }
       guard let expect = expect else {
-        throw "Match succeeded where failure expected"
+        throw "Match of \(test) succeeded where failure expected in \(regex)"
       }
       let capStrs = caps.map { $0 == nil ? nil : String($0!) }
       guard expect.count == capStrs.count else {

      ("abbbe", nil),
      ("accce", nil),
      ("abcbbd", nil))
  }

  func testMatchReferences() {

      }
    } catch {
      if !xfail {
        XCTFail("\(error)", file: file, line: line)
      }
    }
  }
