Advanced En Passant Capture

[dmgolembiowski]

When a pawn advances two squares on its initial move and ends the turn adjacent to an enemy pawn on the same row, it may be captured via en passant by the enemy pawn as if it had moved only one square. This capture is legal only on the move immediately following the pawn's advance. So, construct a valid game state, verify en passant capture is possible, and compare the actual outcome of the move taken on the GameState against the theoretical expectation.