Can solve {"op":"~","inner":{"op":"*","left":40,"right":{"op":"~","inner":{"op":"~","inner":{"op":"~","inner":{"op":"~","inner":4}}}}}} without throwing

Returns a list of instructions which contains the minimum viable items

expected [Function] to not throw an error but 'AssertionError: Result is too short: expected 1 to be at least 6' was thrown

Result is too short is clearly not what minimum viable items, as stated by the test block, means, so it's just plain confusing. It's also a very roundabout and kinda unreliable way of testing the actual requirement of not folding constants.

If you want to check constants are not folded, you'd at least need to reconstruct the AST and check if they're structurally equal. That's the only way.

should correctly split negative numbers
expected [ -1, -0 ] to deeply equal [ -1, 0 ]

-1 + -0 == -1 too.

Dividing an integer is not a novel idea.