Enhanced retain.js tests by fake timers

[gnought]

No description provided.

[gnought]

@mcollina looks good?

[mcollina]

lgtm

[coveralls]

Pull Request Test Coverage Report for Build 8b42d25394f9c6a0c904a28ed1d5e64ed1ef8543-PR-444

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 99.72%

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Totals
Change from base Build 37b04b7778d0ebcd410ffda33787f92be975c1da:	0.0%
Covered Lines:	762
Relevant Lines:	762

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💛 - Coveralls