python unittest ModuleNotFoundError: No module named

I tried to crate simple Python project with flask and unittest. Structure is quite simple:

classes  |-sysinfo      |static      |templates         |- index.html         |- layout.html      |__init__.py      |sysinfo.py      |printinfo.py  tests  |test_sysinfo.pyREADME.mdrequirments.txt

Very simple class in printinfo.py:

 #!/usr/bin/pythonimport psutilimport jsonclass SysInfo:.......    def displayInfo(self):        .......        return json.dumps(self.__data)

And simple flask server run with sysinfo.py:

from flask import Flask, flash, redirect, render_template, request, session, abortfrom printinfo import SysInfoimport jsonobj1 = SysInfo("gb")app = Flask(__name__)@app.route('/')def index():    var = json.loads(obj1.displayInfo())    return render_template('index.html',**locals())@app.route('/healthcheck')def healthcheck():    return "Ok"@app.route("/api/all")def all():    return obj1.displayInfo()if __name__ == '__main__':   app.run(host='0.0.0.0', port=80)del obj1

I run it with python sysinfo.py staying in classes/sysinfo folder and everything works ok.

So I decided to run unittest for my application. Put in classes/tests ( also tried classes/sysinfo/tests) file test_sysinfo.py with code:

import unittestimport printinfofrom sysinfo import sysinfoimport jsonimport sysclass TestFlaskApi(unittest.TestCase):    def setUp(self):        self.app = sysinfo.app.test_client()    def simple_test(self):        response = self.app.get('/health')        self.assertEqual(            json.loads(response.get_data().decode(sys.getdefaultencoding())),            {'healthcheck': 'ok'}        )if __name__ == "__main__":    unittest.main()

And when I started it I can see error:

Error Traceback (most recent call last):   File "\Python\Python37-32\lib\unittest\case.py", line 59, in testPartExecutor     yield   File "\Python\Python37-32\lib\unittest\case.py", line 615, in run     testMethod()   File "\Python\Python37-32\lib\unittest\loader.py", line 34, in testFailure     raise self._exception ImportError: Failed to import test module: test_sysinfo Traceback (most recent call last):   File"\Python\Python37-32\lib\unittest\loader.py", line 154, in loadTestsFromName     module = __import__(module_name)   File "\classes\sysinfo\tests\test_sysinfo.py", line 2, in <module>     import printinfo ModuleNotFoundError: No module named 'printinfo'

I read several articles, some topics here on StackOverflow for my understanding it's related to project structure. I tried to create setup.py and setup.cfg. I managed to start it with this setup, but test still didn't work.

Could you please help me with minimum setup applicable for my case? All the material I found had written for specific case or too general. I cannot apply it for my case.