Minecraft – How to detect minecraft item (any fern) in correct item frame and in correct rotation (1.13)

Items don't, by default, have any identifying feature that would separate them from another item of the same type. You can swap the position of two levers around in your inventory and your inventory will be in the exact same state.

If you want to test that a specific lever is in the frame, you'll need to make something about it unique. For example, you could give the item you want to test for unique Lore:

/give @p lever 1 0 {display:{Lore:["Key"]}}

And then test for it like this;

/testfor @e[type=ItemFrame,x=-322,y=57,z=-61,r=0] {Item:{id:minecraft:lever,tag:{display:{Lore:["Key"]}}},ItemRotation:5b}

Try this if you are in 1.13:

/execute as @p if block -712 58 -1887 minecraft:air run setblock -729 56 -1884 minecraft:redstone_block replace

In 1.12.2 I tried:

execute @p ~ ~ ~ detect -712 58 -1887 air 0 setblock -729 56 -1884 minecraft:redstone_block

and it worked. It only returned that message if there was already a redstone block there. Did you check if there was one or just check the command block? BTW it worked when I used minecraft:air instead of air as well.