Add test to inequality indicators

[asdf8601]

We need introduce new test to inequality indicators.
Find a correct way to test and implement them.
There are different approaches:

• Generate random data and test the result against other package.
• Generate determinist data with a known value.
• Load data generated previously with an indicator calculated, for example, with other software and test against that.

[asdf8601]

The table in the wiki article have some distribution functions with their gini coefficients:

Source: https://en.wikipedia.org/wiki/Gini_coefficient#Continuous_probability_distribution