Naughty KeyboardImpossible dates test values
Dates that do not exist, that are ambiguous, or that are written differently than the field assumes. 12 values, each with what it breaks and what a correct application does instead.
Type them one at a time with AltShiftN
in the palette, or take them all into a script with nkb emit dates-impossible.
30 February
dates-impossible/feb-30
30.02.2026
30.02.2026
- 10 graphemes
- 10 code points
- 10 bytes
- 10 UTF-16 units
- What it breaks
- A date that cannot exist; naive parsers roll it over to the second of March instead of refusing it.
- What a correct application does
- Rejected with a message - never silently moved to another day.
29 February in a non-leap year
dates-impossible/feb-29-non-leap
29.02.2026
29.02.2026
- 10 graphemes
- 10 code points
- 10 bytes
- 10 UTF-16 units
- What it breaks
- Valid in some years and not in others, so the same input is correct or incorrect depending on the year field next to it.
- What a correct application does
- Rejected for non-leap years, with the reason stated.
31 November
dates-impossible/nov-31
31.11.2026
31.11.2026
- 10 graphemes
- 10 code points
- 10 bytes
- 10 UTF-16 units
- What it breaks
- The month-length check that most hand-written validators skip.
- What a correct application does
- Rejected, not rolled over into December.
Day and month in an ambiguous order
dates-impossible/ambiguous-day-month
03/04/2026
03/04/2026
- 10 graphemes
- 10 code points
- 10 bytes
- 10 UTF-16 units
- What it breaks
- The same text means March or April depending on convention, and nothing on screen says which was assumed.
- What a correct application does
- The expected order stated next to the field, or an unambiguous format enforced.
ISO 8601 date
dates-impossible/iso-format
2026-09-06
2026-09-06
- 10 graphemes
- 10 code points
- 10 bytes
- 10 UTF-16 units
- What it breaks
- A field expecting a local format receives the international one, and vice versa; both are legitimate user input.
- What a correct application does
- Both accepted, or one enforced with a visible example.
Year 9999
dates-impossible/year-9999
31.12.9999
31.12.9999
- 10 graphemes
- 10 code points
- 10 bytes
- 10 UTF-16 units
- What it breaks
- The upper end of most date types; often accepted by the interface and rejected by storage.
- What a correct application does
- The same range enforced on both sides.
Year 0000
dates-impossible/year-0000
01.01.0000
01.01.0000
- 10 graphemes
- 10 code points
- 10 bytes
- 10 UTF-16 units
- What it breaks
- Below the range of several date types, and the year zero does not exist in the common calendar.
- What a correct application does
- Rejected with a stated range.
Five-digit year
dates-impossible/year-10000
01.01.10000
01.01.10000
- 11 graphemes
- 11 code points
- 11 bytes
- 11 UTF-16 units
- What it breaks
- Five-digit years break fixed-width parsing and column formats without producing an obvious error.
- What a correct application does
- Rejected with a stated range.
Unix epoch
dates-impossible/epoch-zero
01.01.1970
01.01.1970
- 10 graphemes
- 10 code points
- 10 bytes
- 10 UTF-16 units
- What it breaks
- The zero point of the most common timestamp representation; frequently indistinguishable from "no date set".
- What a correct application does
- Stored and displayed as a real date, distinct from an empty field.
Negative timestamp
dates-impossible/negative-timestamp
-1
-1
- 2 graphemes
- 2 code points
- 2 bytes
- 2 UTF-16 units
- What it breaks
- Dates before the epoch are negative in many representations and are silently rejected or wrapped.
- What a correct application does
- Handled as an ordinary past date, or rejected with the supported range stated.
A date in words
dates-impossible/date-in-words
tomorrow
tomorrow
- 8 graphemes
- 8 code points
- 8 bytes
- 8 UTF-16 units
- What it breaks
- Text in a date field: accepted by lenient parsers, which then produce a different date every day.
- What a correct application does
- Rejected - natural-language dates belong to a deliberate feature, not to a parser's leniency.
Slashes instead of dots
dates-impossible/dots-vs-slashes
06/09/2026
06/09/2026
- 10 graphemes
- 10 code points
- 10 bytes
- 10 UTF-16 units
- What it breaks
- The same date in another separator; forms often accept one and store the other without saying so.
- What a correct application does
- Accepted in both, normalised once, and shown in one consistent form.