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If installed, TestCov will not find dependency tsbuilder anymore,
because setup.py does, at the moment, not properly install that

Based on test data we use - previously, only bogus data was provided.
But there's great value in an example command-line that can actually be tried out
as a 'some test'

Pipenv is complicated to maintain, just use default requirements.txt

When using lcov with gcov in versions < 8, the last else-statement
in a program is always marked as 'covered'.
To avoid this bug, use gcc 8.

Create a step plot for accumulated coverage,
and a bar plot for individual test coverage

Closes #11

Closes #9