DataObjects::ConnectionError: database is locked

When testing using:

bin/rails test

With this code:
https://gist.github.com/igravious/1d5316eca6471af84b9e7216fc665bb5

I'm getting

E

Error:
CreateTriple#test_remote_– explicit_(good):
DataObjects::ConnectionError: database is locked
    lib/tasks/triples.rake:224:in `wrap_create'
    lib/tasks/triples.rake:146:in `block (2 levels) in <main>'
    test/lib/triples_create_test.rb:73:in `block in <class:CreateTriple>'

Any ideas why?

Thanks in advance!