[SemTiOne]

Prior art: #14286.

Pytest reported the wrong extra item when comparing sequences of different lengths. It printed the item past the end of the shorter side. The real extra item sat at the first differing index.
Before:

E     assert [1, 2, 3] == [1, 2, 0, 3]
E       At index 2 diff: 3 != 0
E       Right contains one more item: 3   (wrong: extra item is 0)

After:

E     Right contains one more item: 0

The fix finds a single inserted item by checking whether the tails after the first differing index align, offset by one. It corrects only the single-extra-item case. Multi-item length differences still use the previous "first extra item" message.

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[OKAN-SOFTWARE]

Reviewed commit 886f14b.

The updated message correctly handles cases where a single element was inserted in the middle of an otherwise matching sequence.

However, the new found_diff and len_diff == 1 condition does not distinguish a genuine insertion from a combination of differing values and unequal lengths.

For example:

left = [1, 2, 9]
right = [1, 3]

The new logic reports:

At index 1 diff: 2 != 3
Left contains one more item: 2

But removing 2 produces [1, 9], which still differs from the right-hand sequence. There is no uniquely identifiable inserted element in this example.

The PR description mentions checking whether the remaining elements align after the first difference, but the current implementation only checks found_diff and the length difference.

Could we verify suffix alignment before identifying the first differing element as the extra item?

For example:

• When the left side is longer, check whether left[i + 1:] == right[i:].
• When the right side is longer, check whether right[i + 1:] == left[i:].

If the remaining elements don't align, retaining a more general length-difference message would avoid identifying an unsupported insertion.

A regression test containing both a length difference and unrelated mismatched values would help cover this distinction.

The focused selection logic was checked with the example above. GitHub's test workflow passes; I have not independently run the complete pytest suite.

[SemTiOne]

Done. Thanks for your review.

[OKAN-SOFTWARE]

Thanks for addressing my previous feedback. The updated suffix-alignment check resolves the issue I identified, and the added regression tests cover the problematic cases.

The latest CI checks are passing. Looks good from my side!