Fix mounting accessor write file

[bernhardkaindl]

Test, cover (and fix the method writeFile()) of subclasses of xcp.accessor.MountingAccessor:

• tests/test_mountingaccessor.py: Add testcases for MountingAccessors

  Add test cases testing the methods openAddress(), access() and writeFile() of subclasses of xcp.accessor.MountingAccessor.

• stubs/pyfakefs/fake_filesystem.pyi: Add typing stub for pyfakefs

  Add a typing stub for pyfakefs to avoid having to disable type checking for pyfakefs in tests/test_mountingaccessor.py which uses it to simulate reading and writing arbitrary files.

• xcp/accessor.py: MountingAccessor.writeFile(): use mode="wb"

  Fix MountingAccessor.writeFile() for binary files as checked by the new test in tests/test_mountingaccessor.py: check_binary_write()

• xcp/accessor.py: Fix static analyis warnings for self.location

  Fix static analysis warnings in MountingAccessor by checking self.location to not be None before accessing it:

  • MountingAccessor: self.location changes between str and None
    depending on the state of the MountingAccessor object (initialized,
    started, stopped/finished). The assert lets checkers know it is str
    when it is used in these locations.

[codecov]

Codecov Report

Merging #75 (07d5abd) into master (70b4531) will increase coverage by 2.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #75      +/-   ##
==========================================
+ Coverage   75.56%   77.59%   +2.03%     
==========================================
  Files          21       21              
  Lines        3466     3468       +2     
==========================================
+ Hits         2619     2691      +72     
+ Misses        847      777      -70     

Flag	Coverage Δ
unittest	77.59% <100.00%> (+2.03%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
xcp/accessor.py	86.19% <100.00%> (+19.27%)	⬆️

... and 2 files with indirect coverage changes