add delete support

[sirexeclp]

using correction mode and reverse printing this implements issue #34

[ArchibaldBienetre]

Please have a look at the requirements described in https://github.com/Chaostreff-Potsdam/erika3004/issues/34#issue-545393620

I'd really like there to be some simple test + support for CharacterBasedErikaMock.

Plus: Let's wait for the big upcoming merge of https://github.com/Chaostreff-Potsdam/erika3004/pull/28

[sirexeclp]

First Hardware test was successful. method expects string in reversed order

[ArchibaldBienetre]

@sirexeclp I'm a bit confused, will code tests according to the way I assume the hardware will work.

Generally, I would have assumed

• I type "Hello"
• I call delete_ascii("olle")
  • the device will move back 1 step, delete the o, and so on...
  • the device will end up with the cursor next to the H, ready for typing?

?

That is what I would assume from manual operation of the device.

Seeing the code, though, I think it wil work like so:

• I type "Hello"
• I need to reposition the device above the "o" (move left 1 normal step)
• I call delete_ascii("olle")
  • the device overprints the letters in order
  • the device will end up with the cursor above the H

I will write tests assuming the latter, for now.

From a user's point of view, I'm unsure what they will expect - when in doubt, let's add a comment that clarifies this.

EDIT:

• I added tests :heavy_check_mark:
• curses support may still be buggy - EDIT: done :heavy_check_mark:

The only thing for me to give you green light is verifying the assumptions I coded into the tests.

EDIT: The Erika will behave like the "backspace" key when it is used in reverse print mode. It will move left first, then delete the character that was there, then remain in place.

[ArchibaldBienetre]

"Manual" test script I used to verify delete_ascii works: I just took the unit test + watched that the curses output also works out.

from erika.erika_mock import CharacterBasedErikaMock

with CharacterBasedErikaMock(width=5, height=1, inside_unit_test=True, exception_if_overprinted=False) as my_erika:
    my_erika.print_ascii("Hello")

    my_erika.move_left()
    my_erika.delete_ascii("o")

    my_erika.delete_ascii("lle")

    my_erika.move_right()
    my_erika.print_ascii("elp")
    my_erika.wait_for_user_if_simulated()

EDIT: In retrospect, I guess I could have tested (and automated the test as part of the existing one) using inch(y, x) or `instr(y, x [,n]) EDIT: I automated this check