Should we, and is it possible, to mock the FTP for unit tests ?

[gmaze]

Should closes #248
Start playing with https://github.com/oz123/pytest-localftpserver

[gmaze]

Seems to work like a charm for the FTP server !

I further gave a try to aioresponses to mock HTTP requests to the erddap, argovis, etc ...

def test_Argofetcher():
    # URI to be catched by mocked server:
    uri = 'https://erddap.ifremer.fr/erddap/tabledap/ArgoFloats.nc?data_mode,latitude,longitude,position_qc,time,time_qc,direction,platform_number,cycle_number,config_mission_number,vertical_sampling_scheme,pres,temp,psal,pres_qc,temp_qc,psal_qc,pres_adjusted,temp_adjusted,psal_adjusted,pres_adjusted_qc,temp_adjusted_qc,psal_adjusted_qc,pres_adjusted_error,temp_adjusted_error,psal_adjusted_error&platform_number=~%221901393%22&distinct()&orderBy(%22time,pres%22)'
    with aioresponses() as m:
        # Set up the expected data to return when this uri will be requested with aiohttp: 
        with open('test_data/ArgoFloats_aa81_6de2_3b5c.nc', mode='rb') as file:
            data = file.read()
        m.get(uri, body=data)

        # Move on to regular unit testing:
        ds = ArgoDataFetcher(src='erddap').float(1901393).to_xarray()
        assert isinstance(ds, xr.Dataset)

Where the test_data/ArgoFloats_aa81_6de2_3b5c.nc file is the response to the uri request.

This seems to work as well ! The ArgoDataFetcher send the http request using a fsspec httpstore but it is catched by aioresponses and the local netcdf file content.

But this method requires to have all the "expected" data stored somewhere, and I don't know where to put these.

[gmaze]

So I implemented a mocked FTP server using https://github.com/oz123/pytest-localftpserver.
It's a fixture with a module scope and loaded by conftest.py, so it's available to any tests.

The mocked FTP is populated with all content from the tutorial gdac dataset (fetcher from the argopy-data repo)

The mocked FTP will not catch all requests to any FTP server. One has to point toward the mocked ftp server to use it.

The only modification required in tests, are on those using the ftpstore to call the GDAC.
The host argument for the ftpstore or the Data/Index fetchers is given by the global variable pytest.MOCKFTP.
(It can't be hard coded because the port number can changed from one tests session to another)

[gmaze]

I will merge for the FTP fix to close #248
and will make a new PR to mock the erddap ...