The test is probably missing a constraint check.
sqlite-src-3330000$ cat bug.sh
make distclean
./configure CFLAGS="-DSQLITE_OMIT_UTF16"
make testfixture
cd test
../testfixture permutations.test extraquick numcast.test
sqlite-src-3330000$ ./bug.sh
rm -f *.lo *.la *.o sqlite3 libsqlite3.la
...
numcast-utf8.0...
! numcast-utf8.0 expected: [utf8]
! numcast-utf8.0 got: []
numcast-utf8.1.1... Ok
numcast-utf8.1.2... Ok
numcast-utf8.2.1... Ok
numcast-utf8.2.2... Ok
numcast-utf8.3.1... Ok
numcast-utf8.3.2... Ok
numcast-utf8.4.1... Ok
numcast-utf8.4.2... Ok
numcast-utf8.5.1... Ok
numcast-utf8.5.2... Ok
numcast-utf8.6.1... Ok
numcast-utf8.6.2... Ok
numcast-utf8.7.1... Ok
numcast-utf8.7.2... Ok
numcast-utf8.8.1... Ok
numcast-utf8.8.2... Ok
numcast-utf16le.0...
! numcast-utf16le.0 expected: [utf16le]
! numcast-utf16le.0 got: []
numcast-utf16le.1.1... Ok
numcast-utf16le.1.2... Ok
numcast-utf16le.2.1... Ok
numcast-utf16le.2.2... Ok
numcast-utf16le.3.1... Ok
numcast-utf16le.3.2... Ok
numcast-utf16le.4.1... Ok
numcast-utf16le.4.2... Ok
numcast-utf16le.5.1... Ok
numcast-utf16le.5.2... Ok
numcast-utf16le.6.1... Ok
numcast-utf16le.6.2... Ok
numcast-utf16le.7.1... Ok
numcast-utf16le.7.2... Ok
numcast-utf16le.8.1... Ok
numcast-utf16le.8.2... Ok
numcast-utf16be.0...
! numcast-utf16be.0 expected: [utf16be]
! numcast-utf16be.0 got: []
numcast-utf16be.1.1... Ok
numcast-utf16be.1.2... Ok
numcast-utf16be.2.1... Ok
numcast-utf16be.2.2... Ok
numcast-utf16be.3.1... Ok
numcast-utf16be.3.2... Ok
numcast-utf16be.4.1... Ok
numcast-utf16be.4.2... Ok
numcast-utf16be.5.1... Ok
numcast-utf16be.5.2... Ok
numcast-utf16be.6.1... Ok
numcast-utf16be.6.2... Ok
numcast-utf16be.7.1... Ok
numcast-utf16be.7.2... Ok
numcast-utf16be.8.1... Ok
numcast-utf16be.8.2... Ok
numcast.test-closeallfiles... Ok
numcast.test-sharedcachesetting... Ok
Time: numcast.test 8 ms
Memory used: now 24 max 57688 max-size 48000
Allocation count: now 1 max 71
Page-cache used: now 0 max 0 max-size 1032
Page-cache overflow: now 0 max 1032
SQLite 2020-08-14 13:23:32 fca8dc8b578f215a969cd899336378966156154710873e68b3d9ac5881b0ff3f
3 errors out of 54 tests on e5-1650 Linux 64-bit little-endian
!Failures on these tests: numcast-utf8.0 numcast-utf16le.0 numcast-utf16be.0
All memory allocations freed - no leaks
Memory used: now 0 max 57688 max-size 48000
Allocation count: now 0 max 71
Page-cache used: now 0 max 0 max-size 1032
Page-cache overflow: now 0 max 1032
Maximum memory usage: 57688 bytes
Current memory usage: 0 bytes
Number of malloc() : -1 calls
sqlite-src-3330000$