I'd expect this to speed up the test suite

Describe the feature you'd like
Now the byexample dropped support for Python 3.5 we can improve the code using the f-strings that appeared in Python 3.6

For example:

var1 = 12
msg1 = "Message using old C-like style: %s" % var1
msg2 = "Message using old format-like style: {}". format(var1)

Things like that could be written as

msg3 = f"Message using th