Add test coverage of splitter function in project tree

tests/test_core/test_core_doctools.py

@@ -27,9 +27,7 @@ from shutil import copyfile
 from mock import causeOSError
 from tools import C, buildTestProject, cmpFiles
 
-from novelwriter.core.project import NWProject
-from novelwriter.core.doctools import DocMerger, DocSplitter
-from novelwriter.core.document import NWDoc
+from novelwriter.core import NWProject, DocMerger, DocSplitter, NWDoc
 
 
 @pytest.mark.core