Fix string formatting in "dummy handlers"

[lvalerom]

Some of the strings in the "dummy handlers" were not properly formatted, as seen below:

# Notice that the parenthesis here are incorrect
ValueError("Method '{}' is not invoked. (Invoked method \
           is '{}'.)").format(method, self._invokedMethod)

As discussed here this PR fixes the string formatting of these modules and changes said formatting to f-strings:

ValueError(f"Method '{method}' is not invoked. (Invoked method "
           f"is '{self._invokedMethod}').")

[codecov]

Codecov Report

Merging #2361 (80883cf) into main (82136f4) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #2361   +/-   ##
=======================================
  Coverage   63.17%   63.17%           
=======================================
  Files         132      132           
  Lines       17187    17187           
=======================================
  Hits        10858    10858           
  Misses       6329     6329           

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[bsipocz]

I think we don't need the return values, otherwise it look all very nice.

[bsipocz]

Does this return value have any effect? As far as I see there are no asserts for the tests, so unless an exception is raised anywhere the tests using check_call would pass.

[lvalerom]

I noticed that as well but I left them just in case. But since you brought it up I'll remove them. I double checked the code and they're never called expecting them to return anything.

[bsipocz]

Thanks @lvalerom!