Test Driven Development with OSGi

A Practical Overview

Test Driven Development

1. Write test

2. Write code

3. Make it pass

OSGi Deployment

3. Watch it fail with error $%^#@

2. Deploy on OSGi

1. Working code

Rod Johnson from Spring Source on OSGi, Things I wish I knew…

• Over-invested in OSGi for 2 years

• Seduced by a technology in search of a problem

• Clever technology but didn’t solve most customers pressing problems

• Spent millions that could have been spent elsewhere

My take: OSGi is like EJB2.0, a 3.0 incarnation is desperately needed.

OSGi

Does investing in OSGi pay off?

OSGi is not easy to use and at the end of the day or year depending on how long it takes to get things working, its value is hard to see. This is why:• Your application will not be more modular overall, on the contrary,

It ends up being not isolated from other applications since it is a share everything instead of share nothing architecture.

• Versioning is pushed further down the stack, you wrestle with maven transitive dependencies during build only to do that again at runtime in OSGi.

• Most libraries are designed to work as libraries in the application classloader not as bundles with their own classloader.

• OSGi is a dynamic service deployment framework (if you need one). It is good for building platforms and for plugin architectures like Eclipse where third party developers need to be sandboxed.

How to work successfully with OSGi

• Don’t develop directly against OSGi or have that in your frequent development cycle, it is mostly a deployment environment.

• You can deploy on jetty inside a test just like the one running inside OSGi without the overhead.

• Use spring dynamic modules vs blueprint to keep bean config separate from osgi config

• Treat configuration as code and use Functional tests with mocks if necessary

Develop-Deploy-Test Cycle

Develop Develop

Continuous Integration

Test Test

Test2Test1 Test3

Resolve failed test

It wasn’t me!

Source control

Short circuit deploy by embedding test container.

PlansProgress Blockers

Scrum

update update

checkin1+2

A word about testing

• Don’t write unit tests that instantiate classes as singletons, write functional tests that instantiate classes like they are configured.

• TDD helps you develop the API and test its implementation using the proper contract.

• Reduce the surface area of the API.

• Remember the API is like a wide angle lens the narrower the focal length the wider the scene of the implementation.

OSGi Service Pattern

API

Impl

Client

1. Register impl for intf<osgi:service… />

2. Lookup impl of intf<osgi:reference filter=… />

Export-Package

Import-Package

Import-Package

OSGiService Registry

When to use mocks

• Use mocks when no alternative. For example, try not to mock the persistence layer but replace with in-memory hsql database so that your ORM and spring configuration are tested.

• OSGi services can easily be mocked using their service interface.

• Use spring to rewire mocks in.

Client running against OSGi

Manager Service

OSGi

AuthService

Hibernate/OpenJpa

My Service

Postgres

Service Client

Separate classloaders

Test running against Jetty

Mock Manager Service

Jetty

Mock AuthService

Hibernate/OpenJpa

My Service

Service Test

One classloader

InMemHSQL

Code Coverage

• Few functional tests can provide good code coverage without skewing the results or making it impossible to refactor and identify dead code.

• The lack of code-coverage over a class is also valuable information. For example missing coverage on an exception class means missing negative test cases.

• You wouldn’t test by throwing exceptions from a unit test, that would be worst than having no tests because it masks the need for one.

• Unit tests should follow the same logic.

Alternatives

• Focus more on value add services and less on the platform. Services like identity and access management etc

• Micro-services Architecture with a private PaaS to bring services together and scale from private to public clouds

• Use platform as a service like Apache Stratosand deployment container like Docker.io

• And/Or OSGi (not exclusive technologies)

Microservices Architecture

Service1 Service2 Service3 Service4

local store

Analytics engine

Workflow Message

Broker

Report engine

STAGE

PROCESS

GENERATE

API Gateway Service Registry

PaaS

requ

est

req

ue

st

App1 App2

Docker container Services Engine Shared store

Cache

Workflow

Sample Project

• The Sample project demonstrate a layered project that can be deployed on an OSGI container like Karaf without compromising its ability to run on an embedded container like jetty hosted inside an IDE or as part of a build and test cycle performed by maven.

• The examples demonstrate the use of functional unit tests that invoke the services via their restful interfaces over HTTP achieving a complete assertion of their logic and configuration via spring and cxf.

• Source: https://github.com/ielian

Fini