Field A 	Field B		Remarks			
1000		X		these 3 rows are valid as there is only one X populated over field B by field A 			
1000						
1000						
						
1009		X		this row is valid as there is one X populated over field B by field A			
						
1010		X		these 3 rows are invalid because there are two Xs populated over field B.   these 3 rows are expected to be outputted 			
1010		X					
1010						
						
1020				these 3 rows are invalid because there is no X populated over Field B. these 3 rows are expected to be outputted. 			
1020						
1020						
						
1030				this row is invalid because there is no X populated over field B. this row is expected to be outputted.