Magnus Härlinmagnus.harlin@iptor.com@MagnusHarlin

What is testability?Repeatable - You should be able to expect the

outcome for known inputsEasy to writeEasy to understandFast

Value of automated testingReduce the time coding + debugging +

testingGives you better maintainabilityQuick feedback mechanismTests as documentation

Comparison

the ease of developing in one code base compared to another

Separation of ConcernsReadabilityLess complexityHigher cohesionLower coupling

Isolate the ugly stuff (infrastructure)    Db-access    Active Directory    Web services    Configuration files

Not isolated

InterfaceRefers to a set of named operations that can be

invoked by clients

public class OrderManager{

public void ProcessOrder(Order order){

OrderRepository orderRepository = new OrderRepository();orderRepository.ProcessOrder(order);

}}

public class OrderManager{

public void ProcessOrder(Order order){

IOrderRepository orderRepository = new OrderRepository();orderRepository.ProcessOrder(order);

}}

public void ProcessOrderAgainstService(Order order){

IOrderRepository orderRepository = new OrderService();orderRepository.ProcessOrder(order);

}

public void ProcessOrder(Order order){

IOrderRepository orderRepository = new OrderRepository();orderRepository.ProcessOrder(order);

}

Dependency Injection (DI)

Instead of a class creating its own dependencies,

its dependencies are inserted into it.

Business LayerData Layer Interface

Data Layer

Service Layer

MockingUse mock object as placeholders for classes

that don’t yet existDon’t mock chatty interfacesFake objects with return and pre-canned

values

Small Tests Before Big TestsSmall focused test will tell you where

something is wrongFast and accurate feedback loopsBoth big (end to end) and small test are

important

The Gateway PatternEncapsulate access to external services by

encapsulating the implementation with interfaces

Object that encapsulates external system

Questions

The big picture - ConclusionTestable system will change your design. There are times when a design decision is

made only to enable testingTestability goes hand in hand with classical

definition of good design - high cohesion, low coupling and separation of concerns

Design for testability gives you maintainability