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.

[github-actions]

Thank you for your contribution. Unfortunately, this PR has been inactive for 90 days (see PR stuck workflow). Of course this is not the final word. The PR can become unstuck, for example, by reengaging in the discussion, answering open questions, rebasing, or adding new commits to this PR.