Some missing tests:
0) g/./s^@^@ - okay: NULs in commands
1) g/./s/^@/ - okay: NULs in patterns
2) a
hello^V^Jworld
. - okay: embedded newlines in insert mode
3) ed -x - verify: 8-bit clean
4) ed - verify: long-line support
5) ed - verify: interactive/help mode
6) G/pat/ - verify: global interactive command
7) V/pat/ - verify: global interactive command