Add unit tests of comparing score of similar searches

[crazytonyli]

This is more of a bug report than a PR.

I noticed that StringRankedSearch has inconsistent behavior around searching the beginning or ending part of a string.

@kean Do you mind looking at these test cases? A few of them fail, which IMO is unexpected. For example, search "42" in "0042" produces a score of 0.5, but searching it in "XX42" produces a score of 0.8.

Regression Notes

1. Potential unintended areas of impact

2. What I did to test those areas of impact (or what existing automated tests I relied on)

3. What automated tests I added (or what prevented me from doing so)

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding unit tests for my changes.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

Testing checklist:

• WordPress.com sites and self-hosted Jetpack sites.
• Portrait and landscape orientations.
• Light and dark modes.
• Fonts: Larger, smaller and bold text.
• High contrast.
• VoiceOver.
• Languages with large words or with letters/accents not frequently used in English.
• Right-to-left languages. (Even if translation isn’t complete, formatting should still respect the right-to-left layout)
• iPhone and iPad.
• Multi-tasking: Split view and Slide over. (iPad)

[dangermattic]

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[kean]

Hmm, there seems to be some issue with WordPressSharedTests. The WordPressShared isnt' configured to run it when you open it from the main Xcode project.

[kean]

XCTAssertEqual(score("00_42", "42"), score("XX_AB", "AB"), accuracy: 0.1)

The issue is with the following rule:

else if term[termIndex].isLetter != input[input.index(before: matchIndex)].isLetter {
                    score += 0.8 // Bonus: letter followed by non-letter or the other way around
                }

It heavily skews towards letter followed by non-letters. It was originally designed for searching in the list of full names and tags. This makes sure that if you search for "app" in "#john-appleseed", you get a high score. I'm not entire sure how to address it, yet, but it needs the same or similar bonus point for numbers.

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XCTAssertEqual(score("00AB", "AB"), score("XXAB", "AB"), accuracy: 0.1)

The score in "XXAB" being lower than in "00AB" makes sense to me because of the previous rules, but since there is an exact "contains" match, it should definitely has a score higher than 0.5.