Constant PREVOUTS_CHAIN_HEIGHT

pub const PREVOUTS_CHAIN_HEIGHT: usize = 4;

The chain length for most zebra-chain proptests.

Most generated chains will contain transparent spends at or before this height.

This height was chosen a tradeoff between chains with no spends, and chains which spend outputs created by previous spends.

The raw probability of having no spends during a test run is:

shielded_input = shielded_pool_count / pool_count
expected_transactions = expected_inputs = MAX_ARBITRARY_ITEMS/2
shielded_input^(expected_transactions * expected_inputs * (PREVOUTS_CHAIN_HEIGHT - 1))

This probability is approximately 3%. However, proptest generation and minimisation strategies can create additional chains with no transparent spends.

To increase the proportion of test runs with proptest spends, increase PREVOUTS_CHAIN_HEIGHT.