When you override a method, the signature must match exactly, and in particular, the argument types must be exactly the same. Otherwise, what you're doing is defining a new method altogether.
JUnit uses the standard equals(Object) inherited from java.lang.Object, but you haven't actually overridden that method; instead you've overloaded it, or defined a new method with the same name. The inherited version is still available, though, and that's what JUnit is using.
Whenever you override equals(), it should look like
Finally, note that whenever you override equals(), you should override hashCode(), too -- or your class won't work properly in many of the standard container classes, or in other situations. See the Javadoc for equals() and hashCode() in java.lang.Object for details.