index_stepdown_init.js depends on finding "IndexBuildAborted: Index build aborted: " in the server's error message logging. However, the particular error message that the stepdown interruption produces is not limited to the IndexBuildsCoordinator/MultiIndexBlock code. For example, the error message can be produced by the repl code layer.

One solution is to just require "Index build failed", which we prepend to all index build failures at the higher level. Otherwise, all possible replication error messages must be handled in the JS test. For example, the test failure prompting this ticket had a NotMaster error; and there may be other possible error messages

See the linked test failure for specifics.