Problem

Once one has reproduced an abi test failure, there's this suggestion in the log output (just an example):
Confirm the diff by rerunning before and after this test failed with SOLANA_ABI_DUMP_DIR!', runtime/src/serde_snapshot/tests.rs:285:5

Proposed Solution

Three suggestions:

1. have the tests make the DUMP_DIR directory if the env var is set. When the variable is set and the directory doesn't exist, nothing happens. Maybe even always dump for ABI (there's always farf)
2. remove the exclamation point from the log message
3. clarify the steps necessary to compare ABIs (with examples)