what's the "test" acording to clarisse to tell if someone is in love? What result did she get? what was montag's result accurate?

From the text:

"I guess it's the last of the dandelions this year. I didn't think I'd find one on the lawn this late. Have you ever heard of rubbing it under your chin? Look." She touched her chin with the flower, laughing.

"Why?"

"If it rubs off, it means I'm in love. Has it?"

He could hardly do anything else but look.

"Well?" she said.

"You're yellow under there."

"Fine! Let's try YOU now."

"It won't work for me."

"Here." Before he could move she had put the dandelion under his chin. He drew back and she laughed. "Hold still!"

She peered under his chin and frowned.

"Well?" he said.

"What a shame," she said. "You're not in love with anyone."

The dandelion text shows that Clarisse is in love and Montag is not. I'd say it's pretty accurate on Montage's part.