Pretty print with unit and physical suffix II
The computation of postdecimal can be simplified to postdecimal = max(precision - predecimal, 0).

eng_format needs a docstring.

On self.seq:


It needs a meaningful name like examples.
It should be local to test_eng_format, since that's the only place it's used.
It can be built in one expression, without mutation:

examples = [(0.002777, 'V', 3, '2.78 mV'),
            (0.02777, 'V', 3, '27.8 mV'),
            ...]

However, looping over a list of test cases is less readable than a bunch of self.assertEqual(eng_format(-0.1, 'A', 6), '-100.000 mA') calls.


test_eng_format should not print all its test cases. Tests should be silent unless they fail.