feat: write some highlevel code

wfassoc/tests/concept.rs

@@ -35,6 +35,7 @@ fn test_ext_parse() {
     }
 
     ok_tester(".jpg", "jpg");
+    err_tester(".");
     err_tester(".jar.disabled");
     err_tester("jar");
 }
@@ -247,6 +248,7 @@ fn test_file_name() {
     }
 
     ok_tester("GoodExecutable.exe");
+    err_tester("");
     err_tester("*.?xaml");
     err_tester(r#"\\\lol///"#);
 }