Dialyzer check only the first case of the function

Question

Why does Dialyzer check only the first case of the function?

-spec f(integer()) -> integer().
f(0) -> 0;
f(_) -> test.

Proceeding with analysis... done in 0m0.25s done (passed successfully)

The version with "case" also passes the check:

-spec f(integer()) -> integer().
f(N) -> 
    case N of
      0 -> 1;
      _ -> test
    end.

Dialyzer version is 4.4.3

Answer 1

If passes, because you have just told it what the function is supposed to do. If you try and call the function with different arguments from the specification, then you would get a warning:

test() -> f(not_an_integer).

gives the dialyzer output:

   f.erl:8:13: The call f:f    
         ('not_an_integer') breaks the contract.   
          (integer()) -> integer()