I’ve been through the other answers, tried everything, and I’m still seeing this error.
My directory structure is:
package

├── __init__.py
├── app.py
├── pytest.ini
├── sdtp
│   ├── __init__.py
│   ├── sdtp_filter.py
│   ├── sdtp_table.py
│   └── sdtp_utils.py
├── sdtp_server
│   ├── __init__.py
│   ├── sdtp_server.py
│   └── table_server.py
├── setup.cfg
├── setup.py
└── tests
├── __init__.py
├── conftest.py
├── pytest.ini
├── test_sdtp_filter.py
├── test_sdtp_server.py
├── test_sdtp_table.py
├── test_sdtp_table_and_filter.py
├── test_sdtp_utils.py
└── test_table_server.py

pytest.ini is

[pytest]
pythonpath = /workspaces/sdtp

conftest.py is:

#
# conftest.py
import sys
from os.path import dirname as d
from os.path import abspath, join
root_dir = d(d(abspath(__file__)))
sys.path.append(root_dir)

The root level init.py is:

from sdtp.sdtp_utils import InvalidDataException
from sdtp.sdtp_utils import SDTP_BOOLEAN, SDTP_DATE, SDTP_DATETIME, SDTP_NUMBER, SDTP_PYTHON_TYPES, SDTP_SCHEMA_TYPES, SDTP_STRING, SDTP_TIME_OF_DAY
from sdtp.sdtp_utils import type_check, check_sdtp_type_of_list, jsonifiable_value,  jsonifiable_row, jsonifiable_rows, jsonifiable_column, convert_to_type, convert_list_to_type, convert_row_to_type_list, convert_rows_to_type_list, convert_dict_to_type
from sdtp.sdtp_filter import SDTP_FILTER_OPERATORS, SDTP_FILTER_FIELDS, check_valid_spec, SDTPFilter
from sdtp.sdtp_table import SDTPTable, SDTPFixedTable, DataFrameTable, RowTable, RemoteCSVTable, RemoteSDTPTable
from sdtp_server.table_server import Table, TableServer, TableNotAuthorizedException, TableNotAuthorizedException, ColumnNotFoundException
from sdtp_server.table_server import build_table_spec
from sdtp_server.sdtp_server import sdtp_server_blueprint

The error is:

vscode ➜ /workspaces/sdtp (main) $ pytest -vvv tests/test_sdtp_utils.py
ImportError while loading conftest '/workspaces/sdtp/tests/conftest.py'.
__init__.py:9: in <module>
    from sdtp.sdtp_utils import InvalidDataException
E   ModuleNotFoundError: No module named 'sdtp.sdtp_utils'

Further, I added:

import sys
print(sys.path)

to the init.py file (just before the ImportError) and got this result:

['/workspaces', '/workspaces/sdtp', '/opt/conda/bin', '/opt/conda/lib/python311.zip', '/opt/conda/lib/python3.11', '/opt/conda/lib/python3.11/lib-dynload', '/opt/conda/lib/python3.11/site-packages']

the imports are in /workspaces/sdtp/sdtp, and that has an init.py file, so it’s (a) on the path; and (b) a module, and (c) it’s found just before the import error
Moreover

$ python
> import __init__
> SDTP_BOOLEAN
'boolean'

works just fine, so when Python is run directly there is no ImportError.

I added conftest.py and pytest.ini after reading the answers here: ModuleNotFoundError with pytest

Can anyone tell me what’s going on?

I tried:

1. Running python native (worked fine)
2. Printing sys.path (got what I expected)
3. Adding conftest.py and pytest.ini (no effect)