SEE! LOL Gandalf was certain but it was still not proved - this was the last test before he could know for absolute sure this was Thee One Ring. But he had no fear of touching it, and he certainly did not drop it into Frodo's hand *hoping* it was cool. He tested that himself first!"How long have you known all this?" asked Frodo again.
"Known?" said Gandalf. "I have known much that only the Wise know, Frodo. But if you mean 'known about this ring,' well, I still do not know, one might say. There is a last test to make. But I no longer doubt my guess."
"...Give me the ring for a moment."
Frodo took it from his breeches-pocket, where it was clasped to a chain that hung from his belt. He unfastened and handed it slowly to the wizard. It felt suddenly very heavy, as if either it or Frodo himself was in some way reluctant for Gandalf to touch it.
Gandalf held it up. It looked to be made of pure and solid gold.
For a moment the wizard stood looking at the fire; then he stooped and removed the ring to the hearth with the tongs and at once picked it up. Frodo gasped.
"It is quite cool," said Gandalf. "Take it."
(I know it's contentious, but I will say it again: for all its faults, the cartoon often gets right per the book what the movie does not. His fear of touching it is a Jackson addition, not from the book)