New global variables were introduced in #11403 and not setting them causes:
0test_bitcoin: wallet/wallet.cpp:4259: CTxDestination GetDestinationForKey(const CPubKey&, OutputType): Assertion `false' failed.
1unknown location(0): fatal error in "importwallet_rescan": signal: SIGABRT (application abort requested)
It’s possible to reproduce the failure reliably by running:
0src/test/test_bitcoin --log_level=test_suite --run_test=wallet_tests/importwallet_rescan
Failures happen nondeterministically because boost test framework doesn’t run tests in a specified order, and tests that run previously can set the global variables and mask the bug.
This is similar to bug #12150. Example travis failure is https://travis-ci.org/bitcoin/bitcoin/jobs/340642010