static PolygonDifferenceFacts()
 {
     _polyPairData        = PolyOperationTestUtility.GeneratePolyPairDifferenceTestDataCollection();
     _differenceOperation = new PolygonDifferenceOperation();
 }
 static PolygonDifferenceFacts() {
     _polyPairData = PolyOperationTestUtility.GeneratePolyPairDifferenceTestDataCollection();
     _differenceOperation = new PolygonDifferenceOperation();
 }