Understand the failure.
Verify the repair.
Small, reproducible software failures. The broken implementation, the fix that didn’t work, and the one that passed—preserved together.
Explore the cases ↓How results are verified ↗WHAT THE ARCHIVE CONTAINS
100840 executable cases. 20168 are open.
Every case records the implementation that fails, the fix that did not work, and the repair that passed its checks—with recorded outputs and source hashes. This release adds 100840 cases across 20168 failure mechanisms and 254 domains.
The open tier gives you the failure and the unsuccessful fix for one case in every mechanism. The remaining 80672 cases, 5 variants per mechanism, are member-only: the verified repair, its recorded checks, and the full fixture suite are held in the member archive. Read the methodology ↗
A RECORD OF WHAT WENT WRONG
Browse the archive / 100840
Duplicate occurrences exclude first · case 01
The operation returns a result or retained state that violates this contract: Return each repeated occurrence after its first appearance, in occurrence order.
Duplicate occurrences exclude first · case 02
The operation returns a result or retained state that violates this contract: Return each repeated occurrence after its first appearance, in occurrence order.
Duplicate occurrences exclude first · case 03
The operation returns a result or retained state that violates this contract: Return each repeated occurrence after its first appearance, in occurrence order.
Duplicate occurrences exclude first · case 04
The operation returns a result or retained state that violates this contract: Return each repeated occurrence after its first appearance, in occurrence order.
Duplicate occurrences exclude first · case 05
The operation returns a result or retained state that violates this contract: Return each repeated occurrence after its first appearance, in occurrence order.
All duplicated members · case 01
The operation returns a result or retained state that violates this contract: Return every occurrence of values that occur more than once.
All duplicated members · case 02
The operation returns a result or retained state that violates this contract: Return every occurrence of values that occur more than once.
All duplicated members · case 03
The operation returns a result or retained state that violates this contract: Return every occurrence of values that occur more than once.
All duplicated members · case 04
The operation returns a result or retained state that violates this contract: Return every occurrence of values that occur more than once.
All duplicated members · case 05
The operation returns a result or retained state that violates this contract: Return every occurrence of values that occur more than once.
Only singleton members · case 01
The operation returns a result or retained state that violates this contract: Return values whose total occurrence count is exactly one, preserving input order.
Only singleton members · case 02
The operation returns a result or retained state that violates this contract: Return values whose total occurrence count is exactly one, preserving input order.
Only singleton members · case 03
The operation returns a result or retained state that violates this contract: Return values whose total occurrence count is exactly one, preserving input order.
Only singleton members · case 04
The operation returns a result or retained state that violates this contract: Return values whose total occurrence count is exactly one, preserving input order.
Only singleton members · case 05
The operation returns a result or retained state that violates this contract: Return values whose total occurrence count is exactly one, preserving input order.
First element default · case 01
The operation returns a result or retained state that violates this contract: Return the first element, or None only when the list is empty.
First element default · case 02
The operation returns a result or retained state that violates this contract: Return the first element, or None only when the list is empty.
First element default · case 03
The operation returns a result or retained state that violates this contract: Return the first element, or None only when the list is empty.
First element default · case 04
The operation returns a result or retained state that violates this contract: Return the first element, or None only when the list is empty.
First element default · case 05
The operation returns a result or retained state that violates this contract: Return the first element, or None only when the list is empty.
Last element default · case 01
The operation returns a result or retained state that violates this contract: Return the last element, or None only when the list is empty.
Last element default · case 02
The operation returns a result or retained state that violates this contract: Return the last element, or None only when the list is empty.
Last element default · case 03
The operation returns a result or retained state that violates this contract: Return the last element, or None only when the list is empty.
Last element default · case 04
The operation returns a result or retained state that violates this contract: Return the last element, or None only when the list is empty.
Last element default · case 05
The operation returns a result or retained state that violates this contract: Return the last element, or None only when the list is empty.
Second element not second distinct · case 01
The operation returns a result or retained state that violates this contract: Return the second positional element or None if fewer than two elements exist.
Second element not second distinct · case 02
The operation returns a result or retained state that violates this contract: Return the second positional element or None if fewer than two elements exist.
Second element not second distinct · case 03
The operation returns a result or retained state that violates this contract: Return the second positional element or None if fewer than two elements exist.
Second element not second distinct · case 04
The operation returns a result or retained state that violates this contract: Return the second positional element or None if fewer than two elements exist.
Second element not second distinct · case 05
The operation returns a result or retained state that violates this contract: Return the second positional element or None if fewer than two elements exist.
Penultimate element · case 01
The operation returns a result or retained state that violates this contract: Return the penultimate element, or None for lengths zero and one.
Penultimate element · case 02
The operation returns a result or retained state that violates this contract: Return the penultimate element, or None for lengths zero and one.
Penultimate element · case 03
The operation returns a result or retained state that violates this contract: Return the penultimate element, or None for lengths zero and one.
Penultimate element · case 04
The operation returns a result or retained state that violates this contract: Return the penultimate element, or None for lengths zero and one.
Penultimate element · case 05
The operation returns a result or retained state that violates this contract: Return the penultimate element, or None for lengths zero and one.
Drop first not all matching · case 01
The operation returns a result or retained state that violates this contract: Remove exactly the first positional element.
Drop first not all matching · case 02
The operation returns a result or retained state that violates this contract: Remove exactly the first positional element.
Drop first not all matching · case 03
The operation returns a result or retained state that violates this contract: Remove exactly the first positional element.
Drop first not all matching · case 04
The operation returns a result or retained state that violates this contract: Remove exactly the first positional element.
Drop first not all matching · case 05
The operation returns a result or retained state that violates this contract: Remove exactly the first positional element.
Drop last not all matching · case 01
The operation returns a result or retained state that violates this contract: Remove exactly the last positional element.
Drop last not all matching · case 02
The operation returns a result or retained state that violates this contract: Remove exactly the last positional element.
Drop last not all matching · case 03
The operation returns a result or retained state that violates this contract: Remove exactly the last positional element.
Drop last not all matching · case 04
The operation returns a result or retained state that violates this contract: Remove exactly the last positional element.
Drop last not all matching · case 05
The operation returns a result or retained state that violates this contract: Remove exactly the last positional element.
Interior excludes both ends · case 01
The operation returns a result or retained state that violates this contract: Return the positional interior, excluding first and last elements.
Interior excludes both ends · case 02
The operation returns a result or retained state that violates this contract: Return the positional interior, excluding first and last elements.
Interior excludes both ends · case 03
The operation returns a result or retained state that violates this contract: Return the positional interior, excluding first and last elements.
Interior excludes both ends · case 04
The operation returns a result or retained state that violates this contract: Return the positional interior, excluding first and last elements.
Interior excludes both ends · case 05
The operation returns a result or retained state that violates this contract: Return the positional interior, excluding first and last elements.
Even position selection · case 01
The operation returns a result or retained state that violates this contract: Select positions 0,2,4 and so on, retaining duplicates.
Even position selection · case 02
The operation returns a result or retained state that violates this contract: Select positions 0,2,4 and so on, retaining duplicates.
Even position selection · case 03
The operation returns a result or retained state that violates this contract: Select positions 0,2,4 and so on, retaining duplicates.
Even position selection · case 04
The operation returns a result or retained state that violates this contract: Select positions 0,2,4 and so on, retaining duplicates.
Even position selection · case 05
The operation returns a result or retained state that violates this contract: Select positions 0,2,4 and so on, retaining duplicates.
Odd position selection · case 01
The operation returns a result or retained state that violates this contract: Select positions 1,3,5 and so on.
Odd position selection · case 02
The operation returns a result or retained state that violates this contract: Select positions 1,3,5 and so on.
Odd position selection · case 03
The operation returns a result or retained state that violates this contract: Select positions 1,3,5 and so on.
Odd position selection · case 04
The operation returns a result or retained state that violates this contract: Select positions 1,3,5 and so on.
Odd position selection · case 05
The operation returns a result or retained state that violates this contract: Select positions 1,3,5 and so on.
Left rotation one · case 01
The operation returns a result or retained state that violates this contract: Move the first item to the end; empty input remains empty.
Left rotation one · case 02
The operation returns a result or retained state that violates this contract: Move the first item to the end; empty input remains empty.
Left rotation one · case 03
The operation returns a result or retained state that violates this contract: Move the first item to the end; empty input remains empty.
Left rotation one · case 04
The operation returns a result or retained state that violates this contract: Move the first item to the end; empty input remains empty.
Left rotation one · case 05
The operation returns a result or retained state that violates this contract: Move the first item to the end; empty input remains empty.
Right rotation one · case 01
The operation returns a result or retained state that violates this contract: Move the last item to the front; empty input remains empty.
Right rotation one · case 02
The operation returns a result or retained state that violates this contract: Move the last item to the front; empty input remains empty.
Right rotation one · case 03
The operation returns a result or retained state that violates this contract: Move the last item to the front; empty input remains empty.
Right rotation one · case 04
The operation returns a result or retained state that violates this contract: Move the last item to the front; empty input remains empty.
Right rotation one · case 05
The operation returns a result or retained state that violates this contract: Move the last item to the front; empty input remains empty.
Pairwise neighbors overlap · case 01
The operation returns a result or retained state that violates this contract: Emit overlapping adjacent pairs, omitting an incomplete singleton.
Pairwise neighbors overlap · case 02
The operation returns a result or retained state that violates this contract: Emit overlapping adjacent pairs, omitting an incomplete singleton.
Pairwise neighbors overlap · case 03
The operation returns a result or retained state that violates this contract: Emit overlapping adjacent pairs, omitting an incomplete singleton.
Pairwise neighbors overlap · case 04
The operation returns a result or retained state that violates this contract: Emit overlapping adjacent pairs, omitting an incomplete singleton.
Pairwise neighbors overlap · case 05
The operation returns a result or retained state that violates this contract: Emit overlapping adjacent pairs, omitting an incomplete singleton.
Nonoverlapping pairs keep tail · case 01
The operation returns a result or retained state that violates this contract: Split into nonoverlapping pairs and preserve a final singleton.
Nonoverlapping pairs keep tail · case 02
The operation returns a result or retained state that violates this contract: Split into nonoverlapping pairs and preserve a final singleton.
Nonoverlapping pairs keep tail · case 03
The operation returns a result or retained state that violates this contract: Split into nonoverlapping pairs and preserve a final singleton.
Nonoverlapping pairs keep tail · case 04
The operation returns a result or retained state that violates this contract: Split into nonoverlapping pairs and preserve a final singleton.
Nonoverlapping pairs keep tail · case 05
The operation returns a result or retained state that violates this contract: Split into nonoverlapping pairs and preserve a final singleton.
All nonempty prefixes · case 01
The operation returns a result or retained state that violates this contract: Return all nonempty prefixes in increasing length, including the complete list.
All nonempty prefixes · case 02
The operation returns a result or retained state that violates this contract: Return all nonempty prefixes in increasing length, including the complete list.
All nonempty prefixes · case 03
The operation returns a result or retained state that violates this contract: Return all nonempty prefixes in increasing length, including the complete list.
All nonempty prefixes · case 04
The operation returns a result or retained state that violates this contract: Return all nonempty prefixes in increasing length, including the complete list.
All nonempty prefixes · case 05
The operation returns a result or retained state that violates this contract: Return all nonempty prefixes in increasing length, including the complete list.
All nonempty suffixes · case 01
The operation returns a result or retained state that violates this contract: Return all nonempty suffixes in increasing start-position order.
All nonempty suffixes · case 02
The operation returns a result or retained state that violates this contract: Return all nonempty suffixes in increasing start-position order.
All nonempty suffixes · case 03
The operation returns a result or retained state that violates this contract: Return all nonempty suffixes in increasing start-position order.
All nonempty suffixes · case 04
The operation returns a result or retained state that violates this contract: Return all nonempty suffixes in increasing start-position order.
All nonempty suffixes · case 05
The operation returns a result or retained state that violates this contract: Return all nonempty suffixes in increasing start-position order.
Enumeration original position · case 01
The operation returns a result or retained state that violates this contract: Pair each element with its original zero-based position.
Enumeration original position · case 02
The operation returns a result or retained state that violates this contract: Pair each element with its original zero-based position.
Enumeration original position · case 03
The operation returns a result or retained state that violates this contract: Pair each element with its original zero-based position.
Enumeration original position · case 04
The operation returns a result or retained state that violates this contract: Pair each element with its original zero-based position.
Enumeration original position · case 05
The operation returns a result or retained state that violates this contract: Pair each element with its original zero-based position.
Reverse enumeration retains indices · case 01
The operation returns a result or retained state that violates this contract: Visit elements in reverse order while retaining their original indices.
Reverse enumeration retains indices · case 02
The operation returns a result or retained state that violates this contract: Visit elements in reverse order while retaining their original indices.
Reverse enumeration retains indices · case 03
The operation returns a result or retained state that violates this contract: Visit elements in reverse order while retaining their original indices.
Reverse enumeration retains indices · case 04
The operation returns a result or retained state that violates this contract: Visit elements in reverse order while retaining their original indices.
Reverse enumeration retains indices · case 05
The operation returns a result or retained state that violates this contract: Visit elements in reverse order while retaining their original indices.
INSPECTABLE BY DESIGN
Every result has a runnable source.
Runnable implementations with recorded outputs, source hashes, and explicit contracts. Related variants share a failure mechanism and belong together in evaluation splits.
Read the methodology ↗