BASH: [ ] (test) behaves unconformly

Question

In my bash test has an attitude to exit with status 0:

$ test -n && echo true || echo false
-> true

while

$ test -n "" && echo true || echo false
-> false

It means when it doesn't receive any argument at all, it assumes nonzero.

The case -z works properly instead:

$ test -z && echo true || echo false
-> true
$ test -z "" && echo true || echo false
-> true

Is this the expected behavior?

Answer 1

Basically, you are asking test whether the string "-z" is nonempty. It is, so it tells you true. The actual algorithm test uses is:

• 0 arguments:

  Exit false (1).

• 1 argument:

  Exit true (0) if $1 is not null; otherwise, exit false.

• 2 arguments:

  If $1 is '!', exit true if $2 is null, false if $2 is not null.

  If $1 is a unary primary, exit true if the unary test is true, false if the unary test is false.

  Otherwise, produce unspecified results.

...

Quoted from the POSIX test command specification.