How do you debug this error when running bench run-tests

I get the error below when I run bench run-tests. From it I can guess something is missing but what ? Any hints on how to debug this ? I have already cleared off all the json files in my fixtures directory.

Traceback (most recent call last):
  File "/usr/lib/python2.7/runpy.py", line 162, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
  File "/usr/lib/python2.7/runpy.py", line 72, in _run_code
    exec code in run_globals
  File "/home/lowks/frappe-bench/apps/frappe/frappe/utils/bench_helper.py", line 79, in <module>
    main()
  File "/home/lowks/frappe-bench/apps/frappe/frappe/utils/bench_helper.py", line 16, in main
    click.Group(commands=commands)(prog_name='bench')
  File "/home/lowks/frappe-bench/env/local/lib/python2.7/site-packages/click/core.py", line 716, in __call__
    return self.main(*args, **kwargs)
  File "/home/lowks/frappe-bench/env/local/lib/python2.7/site-packages/click/core.py", line 696, in main
    rv = self.invoke(ctx)
  File "/home/lowks/frappe-bench/env/local/lib/python2.7/site-packages/click/core.py", line 1060, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/home/lowks/frappe-bench/env/local/lib/python2.7/site-packages/click/core.py", line 1060, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/home/lowks/frappe-bench/env/local/lib/python2.7/site-packages/click/core.py", line 889, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/home/lowks/frappe-bench/env/local/lib/python2.7/site-packages/click/core.py", line 534, in invoke
    return callback(*args, **kwargs)
  File "/home/lowks/frappe-bench/env/local/lib/python2.7/site-packages/click/decorators.py", line 17, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "/home/lowks/frappe-bench/apps/frappe/frappe/commands.py", line 29, in _func
    ret = f(frappe._dict(ctx.obj), *args, **kwargs)
  File "/home/lowks/frappe-bench/apps/frappe/frappe/commands.py", line 790, in run_tests
    force=context.force, profile=profile)
  File "/home/lowks/frappe-bench/apps/frappe/frappe/test_runner.py", line 39, in main
    ret = run_all_tests(app, verbose, profile)
  File "/home/lowks/frappe-bench/apps/frappe/frappe/test_runner.py", line 74, in run_all_tests
    _add_test(path, filename, verbose, test_suite=test_suite)
  File "/home/lowks/frappe-bench/apps/frappe/frappe/test_runner.py", line 156, in _add_test
    make_test_records(doctype, verbose)
  File "/home/lowks/frappe-bench/apps/frappe/frappe/test_runner.py", line 173, in make_test_records
    make_test_records_for_doctype(options, verbose, force)
  File "/home/lowks/frappe-bench/apps/frappe/frappe/test_runner.py", line 223, in make_test_records_for_doctype
    frappe.local.test_objects[doctype] += make_test_objects(doctype, test_records, verbose)
  File "/home/lowks/frappe-bench/apps/frappe/frappe/test_runner.py", line 265, in make_test_objects
    d.insert()
  File "/home/lowks/frappe-bench/apps/frappe/frappe/model/document.py", line 194, in insert
    self._validate()
  File "/home/lowks/frappe-bench/apps/frappe/frappe/model/document.py", line 341, in _validate
    self._validate_mandatory()
  File "/home/lowks/frappe-bench/apps/frappe/frappe/model/document.py", line 533, in _validate_mandatory
    raise frappe.MandatoryError(", ".join((each[0] for each in missing)))
frappe.exceptions.MandatoryError: parent, parenttype