Hi,
It will help better if you provide the test scenarios/cases that you wish to cover and any background information on them. Also provide information on how you to intend to test them (or have tested for them).
From what you are indicating, it seems that one of your instances failed and only THAT instanced failed over to the standy instance. With your configuration, this seems to be ok (but it seems you were expecting ALL instances to failover).
Remember that "HA" is a very generic term - and can mean different things to different people (e.g. for Apps Arhitect it means his "browser" session should be tolerant to anything happening on the infrastructue). In the realm of DB2, HA can be implemented at the OS level (using clustering s/w or using DB2 HADR technology similar to Oracle's DataGuard). It seems you are using HADR.
The more info you provide the better help we can provide.