Integration Testing: Why? What? & How?

Introduction:
There are various levels of testing:
Unit Testing, Integration Testing, System Testing, Acceptance Testing.
Each level of testing builds on the previous level.

“Unit testing” focuses on testing a unit of the code.
“Integration testing” is the next level of testing. This ‘level of testing’ focuses on testing the integration of “units of code” or components.

How does Integration Testing fit into the Software Development Life Cycle?
Even if a software component is successfully unit tested, in an enterprise n-tier distributed application it is of little or no value if the component cannot be successfully integrated with the rest of the application. Once unit tested components are delivered we then integrate them together. These “integrated” components are tested to weed out errors and bugs caused due to the integration. This is a very important step in the Software Development Life Cycle.

It is possible that different programmers developed different components.
A lot of bugs emerge during the integration step.
In most cases a dedicated testing team focuses on Integration Testing.

Prerequisites for Integration Testing:
Before we begin Integration Testing it is important that all the components have been successfully unit tested.

Integration Testing Steps:
Integration Testing typically involves the following Steps:
Step 1: Create a Test Plan
Step 2: Create Test Cases and Test Data
Step 3: If applicable create scripts to run test cases
Step 4: Once the components have been integrated execute the test cases
Step 5: Fix the bugs if any and re test the code
Step 6: Repeat the test cycle until the components have been successfully integrated

What is an ‘Integration Test Plan’?
As you may have read in the other articles in the series, this document typically describes one or more of the following:

• How the tests will be carried out
• The list of things to be Tested
• Roles and Responsibilities
• Prerequisites to begin Testing
• Test Environment
• Assumptions
• What to do after a test is successfully carried out
• What to do if test fails
• Glossary

How to write an Integration Test Case?
Simply put, a Test Case describes exactly how the test should be carried out.
The Integration test cases specifically focus on the flow of data/information/control from one component to the other.
So the Integration Test cases should typically focus on scenarios where one component is being called from another. Also the overall application functionality should be tested to make sure the app works when the different components are brought together.
The various Integration Test Cases clubbed together form an Integration Test Suite. Each suite may have a particular focus. In other words different Test Suites may be created to focus on different areas of the application.
As mentioned before, a dedicated Testing Team may be created to execute the Integration test cases. Therefore the Integration Test Cases should be as detailed as possible.

Sample Test Case Table:

Test Case ID	Test Case Description	Input Data	Expected Result	Actual Result	Pass/Fail	Remarks

Additionally the following information may also be captured:

• Test Suite Name
• Tested By
• Date
• Test Iteration (One or more iterations of Integration testing may be performed)

Working towards Effective Integration Testing:
There are various factors that affect Software Integration and hence Integration Testing:

1) Software Configuration Management: Since Integration Testing focuses on Integration of components and components can be built by different developers and even different development teams, it is important the right versions of components are tested. This may sound very basic, but the biggest problem faced in n-tier development is integrating the right version of components. Integration testing may run through several iterations and to fix bugs components may undergo changes. Hence it is important that a good Software Configuration Management (SCM) policy is in place. We should be able to track the components and their versions. So each time we integrate the application components we know exactly what versions go into the build process.
2) Automate Build Process where Necessary: A Lot of errors occur because the wrong version of components were sent for the build or there are missing components. If possible write a script to integrate and deploy the components this helps reduce manual errors.
3) Document: Document the Integration process/build process to help eliminate the errors of omission or oversight. It is possible that the person responsible for integrating the components forgets to run a required script and the Integration Testing will not yield correct results.
4) Defect Tracking: Integration Testing will lose its edge if the defects are not tracked correctly. Each defect should be documented and tracked. Information should be captured as to how the defect was fixed. This is valuable information. It can help in future integration and deployment processes.

Summary:
Integration testing is the most crucial steps in Software Development Life Cycle. Different components are integrated together and tested. This can be a daunting task in enterprise applications where diverse teams build different modules and components.

Reference -
http://www.exforsys.com/tutorials/testing/integration-testing-whywhathow.html