[build-an-anchor-leaderboard]: add tests

[ShaunSHamilton]

Some of the user stories for the Build an Anchor Leaderboard integrated project do not have corresponding tests. The original approach I was taking would have made the tests take 5 - 20 min to run, which is not ideal.

As such, it would be ideal if a better testing methodology could be found, whilst still keeping the project permissible; this is not a practice project where a Camper can be told what code to put where, this is an integrated project where Campers just need to accomplish "integrated-style user stories".

Tests

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• The initialize_leaderboard instruction handler should initialize the leaderboard account with the players field set to an empty vector.
• The leaderboard account should be initialized, if it does not already exist.
• The initialization of the leaderboard account should be payed for by the game_owner account.
• The correct amount of space for 5 players should be allocated for the leaderboard account.
• The PDA should be seeded with "leaderboard" and the game_owner public key.
• The game_owner account public key should be asserted to match the game-owner.json file public key.
• The game_owner account owner should be asserted to be the system program.
• The new_game instruction handler should take a String argument.
• The new_game instruction handler should transfer 1 SOL from the user account to the game_owner account.
• The new_game instruction handler should add a new Player to the leaderboard with:
• The username field of the new Player should be set to the String argument.
• The pubkey field of the new Player should be set to the user account public key.
• The score field of the new Player should be set to 0.
• The has_payed field of the new Player should be set to true.
• If the leaderboard is full, the player with the lowest score should be replaced.
• The NewGame game_owner account should be asserted to match the game-owner.json file public key.
• The NewGame game_owner account owner should be asserted to be the system program.
• The add_player_to_leaderboard instruction handler should take a u64 argument.
• The player matching the user account public key should be updated with a score set to the u64 argument.
• The player matching the user account public key should be updated with a has_payed set to false.
• If no player matching the user account public key exists and has payed, an Anchor error variant of PlayerNotFound should be returned.
• The "initializes leaderboard" it block should call the initialize_leaderboard instruction.
• The "initializes leaderboard" it block should assert the leaderboard account equals { players: [] }.
• The "creates a new game" it block should call the new_game instruction with a username argument of "camperbot".
• The "creates a new game" it block should assert the leaderboard account has at least one player.
• The "creates a new game" it block should assert the player has the correct username.
• The "creates a new game" it block should assert the player has the correct pubkey.
• The "creates a new game" it block should assert the player has a hasPayed value of true.
• The "creates a new game" it block should assert the player has a score value of 0.
• The "creates a new game" it block should assert the balance of the user account has decreased by at least 1 SOL.
• The "adds a player to the leaderboard" it block should call the add_player_to_leaderboard instruction with an argument of 100.
• The "adds a player to the leaderboard" it block should assert a player has a score value of 100.
• The "adds a player to the leaderboard" it block should assert a player has a hasPayed value of false.
• The "throws an error when the user has not payed" it block should assert the PlayerNotFound error variant is returned when the user account has not payed.