look in the mefarshim in the begining of hoshea about horaos shaah.
The gemara in Menachos talks about a shayala, and Rebbi says when he sees Eliyahu Hanavi he will ask him. The meyuches L’rashba explains that Eliyahu hanavi used to stop by rebbi and they would ask him all their shayalos.
And the klal lo bashamaim does not apply at all to eliyau hanavi. THere is a very famous teshuvas chasam sofer about eliyahu hanavi malach or enosh. HE discusses this at length. he says that the reason eliyahu hanavi will answer ouur taku and all unanswerede question is becasue he is a person so that klal will not apply. So if eliyahu hanavi tld me it is techailes I will continue to wear it.
The real question is if Eliyahu hanavi tells you that a piece of meat is kosher can you rely on it. Many poskim bring various rayas from throughout shas there are amoraim who pasken based on sod hashem.
About them passing the kla ilan test. Take murex and kla ilan and put them in bleach. The murex will not loose the color at all , while the kla ilan will