Add diff section to report of AssertionFailedError failures

[bechte]

Overview

With this commit, a dependency to https://github.com/java-diff-utils/java-diff-utils is introduced. java-diff-utils is used to create a diff from the expected and the actual result and report it.

See #3139

Open questions:

• Shall we shadow the external library?
• Shall we provide configuration parameters for the console launcher to adjust the markers for "old" (currently: ~) and "new" (currently: **) text.
• Shall we include these changes also into other DetailsPrintingListeners or is it already sufficient for the FlatPrintingListener (I started with this in the sense of a small PoC)?

---

I hereby agree to the terms of the JUnit Contributor License Agreement.

---

Definition of Done

• There are no TODOs left in the code
• Method preconditions are checked and documented in the method's Javadoc
• Coding conventions (e.g. for logging) have been followed
• Change is covered by automated tests including corner cases, errors, and exception handling
• Public API has Javadoc and @API annotations
• Change is documented in the User Guide and Release Notes

[sormuras]

Hi Stefan, thanks for the PR.

Shall we shadow the external library?

Yes, please.

Shall we provide configuration parameters for the console launcher to adjust the markers for "old" (currently: ~) and "new" (currently: **) text.

Let's go with same length for the tags (fixed for the time being): ~ and *

It would be also cool, if the theme of the console launcher could be supported:

• ASCII (~ and *) vs Unicode (for example: — and ⁕ or ﹡)
• with ANSI colors (and strike-through for "old"?) vs. without colors. See Theme and Palette classes for details.

Shall we include these changes also into other DetailsPrintingListeners or is it already sufficient for the FlatPrintingListener (I started with this in the sense of a small PoC)?

Once the layout is settled, all printing listeners should support this new diff feature. Or do you see problems with rendering the diff in other printers than the FlatPrintingListener?

[marcphilipp]

@bechte Do you have time to continue on this?

[marcphilipp]

Superseded by #4017