referrerpolicy=no-referrer-when-downgrade

TEST_RUNTIME_UPGRADE_KEY

cumulus_test_runtime::test_pallet

Constant TEST_RUNTIME_UPGRADE_KEY 

Source 
pub const TEST_RUNTIME_UPGRADE_KEY: &[u8] = b"+test_runtime_upgrade_key+";
Expand description

Some key that we set in genesis and only read in SingleBlockMigrations to ensure that OnRuntimeUpgrade works as expected.