Add simple prop tests

tests/prop.rs

@@ -0,0 +1,15 @@
+use phonenumber::parse;
+use proptest::prelude::*;
+
+proptest! {
+    #[test]
+    fn doesnt_crash(s in "\\PC*") {
+        let _ = parse(None, &s);
+    }
+
+    #[test]
+    fn parse_belgian_phonenumbers(s in "\\+32[0-9]{8,9}") {
+        let parsed = parse(None, &s).expect("valid Belgian number");
+        prop_assert_eq!(parsed.country().id(), phonenumber::country::BE.into());
+    }
+}