Test ChessBoard#king_of_current_player_is_in_check?
Fix ChessBoard#switch_players
Test ChessBoard#switch_players
Test ChessBoard#player_owns_piece_on?
Fix Pawn functions
Test ChessBoard#allowed_to_move_piece_on?
Test ChessBoard#game_over?
Fix runtime error
Test ChessBoard#make_a_move
Test getting game status
Test ChessBoard#promotion?
Test Piece class
Test Queen class
Fix bug in Bishop#valid_move?
Test Bishop class
Test Knight class
Fix Pawn#valid_move?
Test Pawn class
Fix King#castle?
Fix King#attacked_by_a_pawn? and King#attacked_by_a_knight