Testing OSGi is not super easy, but there is a OSS project called Pax-Exam that has an OSGi based test kit.
We use this for other Apache project such as: Camel, ActiveMQ, etc.
There is a pax exam 2.x release which is even better. We have not yet upgrade from 1.x to 2.x in Camel, as its a bit work to do.
The 2.x should be much faster and allows to do in-jvm debugging etc. The 1.x is slow and it fork a jvm for testing. And it downloads a lot of JARs etc.
That was the reason we discovered this as we upgraded camel-zookeeper from 3.3.4 to 3.4.1 and our osgi based test failed.
The regular junit test passed of course.
At Apache Camel we have 2 kind of osgi tests
- karaf feature test 
- osgi unit tests 
The former is just a test that the camel components can be installed in an osgi runtime such as Apache Karaf. This test will frankly bootup Apache Karaf and then do an osgi install of the bundles. That way we can often spot 3rd party JARs which is not OSGi compliant.
The latter is real full blown osgi unit tests, where we use the components and do something.
For a quick test, you may in Zookeeper, have the first kind of test, where you will install zookeeper as a bundle in an osgi runtime, such as apache karaf (it can test with using felix, equinox as osgi framework).
1) - https://svn.apache.org/repos/asf/camel/trunk/tests/camel-itest-karaf/
2) - https://svn.apache.org/repos/asf/camel/trunk/tests/camel-itest-osgi/