Disregard test strings that can be converted to numbers when testing non-numeric strings.

This is a straight oversight in the property. We asserted the proposition "the string contains no NULs implies the string will be rejected," but the test suite found a counterexample: `"0"` contains no NULs and is not rejected.

This is correct behaviour - the string "0" should be converted to the port number 0! So, now the proposition is more complex: "the string contains no NULs and cannot be converted to a number implies the string will be rejected." This closely mirrors the implementation, which isn't fantastic, but I can't see a more succinct and accurate way to frame the property.

1 files changed, 3 insertions, 0 deletions

diff --git a/src/twelve.rs b/src/twelve.rs
index 34b7756..273b17f 100644
--- a/src/twelve.rs
+++ b/src/twelve.rs
@@ -195,6 +195,9 @@ mod tests {
         if env_port.contains("\x00") {
             return TestResult::discard();
         }
+        if env_port.parse::<u16>().is_ok() {
+            return TestResult::discard();
+        }
 
         env_locked(|| {
             env::set_var("PORT", env_port.to_string());