protected List<Class<? extends JavaMigration>> getAdditionalMigrationClasses() {
        return Collections.emptyList();
    }
This gets overridden for testing to allow the test migration to be added in.
Order doesn't matter as the migrations will be ordered by
{@link org.flywaydb.core.api.MigrationVersion} anyway.
stroom-app/src/main/java/stroom/app/db/migration/CrossModuleDbMigrationsModule.java