Test case:
EXECUTE:
1. Create CDI project
2. Create class:

import javax.enterprise.event.Observes;

public class Test {
	public void foo(@Observes String s1, String s2) {
	}
}

3. Be sure that preference JBoss Tools->CDI->CDI Validator->Multiple observing parameters is set to value "Warning"
4. Open class Test in Java Editor
5. Add annotation @Observes to parameter s2
6. Do not save the editor
ASSERT:
annotations @Observes should be marked with problem annotation
EXECUTE: Point mpouse to one of annotations @Observes
ASSERT: Quick Fixes "Add @SuppressWarnings" for method and for parameter should be in Text Hoover