Unit tests readability/maintainability

[sylvlecl]

• Do you want to request a feature or report a bug?

Code improvement

• What is the current behavior?

Unit tests involve a lot of dataframe creation and comparisons. Those dataframes are created using usual factory functions, but it makes them not easily readable nor updatable.

• What is the expected behavior?

We could load dataframes from a textual representation using multiline strings:

# Before
expected = pd.DataFrame(
    index=pd.Series(name='id', data=['VSC1', 'VSC2']),
    columns=['name', 'loss_factor', 'min_q', 'max_q', 'reactive_limits_kind', 'target_v', 'target_q',
             'voltage_regulator_on', 'regulated_element_id', 'p', 'q', 'i', 'voltage_level_id', 'bus_id',
             'connected'],
    data=[
        ['VSC1', 1.1, NaN, NaN, 'CURVE', 300, 400, True, 'VSC2', 10.11, -512.081, 739.27, 'S1VL2', 'S1VL2_0', True],
        ['VSC2', 1.1, -350, 400, 'MIN_MAX', 1, 2, False, 'VSC1', -9.89, -120, 170.032, 'S2VL1', 'S2VL1_0', True]
    ]
)

# After
expected_str = """
  id name  loss_factor  min_q  max_q reactive_limits_kind  target_v  target_q  voltage_regulator_on regulated_element_id     p        q       i voltage_level_id  bus_id  connected
VSC1 VSC1          1.1    NaN    NaN                CURVE       300       400                  True                 VSC2 10.11 -512.081 739.270            S1VL2 S1VL2_0       True
VSC2 VSC2          1.1 -350.0  400.0              MIN_MAX         1         2                 False                 VSC1 -9.89 -120.000 170.032            S2VL1 S2VL1_0       True
"""

• What is the motivation / use case for changing the behavior?

Mostly understanding of tests and convenience to update them.

[sylvlecl]

Started in #408, using util.dataframe_from_string method