Refactored import statements to use org.junit.Assert

[tfr42]

This PR contains minor improvements of the usage of JUnit API.

• refactored import statements to use org.junit.Assert instead of deprecated junit.framework.Assert type
• uses assertEquals for double values with a delta of 0.01d, see https://junit.org/junit4/javadoc/4.13/org/junit/Assert.html#assertArrayEquals(double[],%20double[],%20double)
• upgraded junit to 4.13.2 (see related PR Bump junit from 4.12 to 4.13.1 #1089)

[tfr42]

Introduce constants for different units and measures.

[stephanr]

From a programmer's point of view it would be nice to use general available constant for most cases and only a local constant if required.
It might also be interesting to derive the general constant from the value previously used by JUnit.