My test-driven experiments to learn solidity.

npm install

npx truffe test

What happens when you cast to a contract passing the wrong address?

If the contract has the same ABI, or even extra state variables, the cast will work. If the contract is missing a state variable, it will fail. If the address is an externally owned account, it will fail.

When is the parent constructor implicitly called?

When the constructor of the parent has no arguments. If the constructor of the parent has arguments and it is not explicitly called on the child, an error is raised: The contract code couldn't be stored, please check your gas amount.

How to use a modifier from another contract?

Inherit from the other contract.

Is it possible to use a modifier from a library?

No, this is not implemented on solidity. See ethereum/solidity#2467

What happens if you access the element after the last one? It fails with invalid opcode.

What happens if you increase the length of an array? It fills the new elements with zero values, even if there were other values in those positions before.

What happens if you try to add an element to an index out of bounds? It fails with invalid opcode.