Integration Testing Outline

Cons: 

It can require creating stubs for tests and thus get time-consuming.

Top-down Integration Testing

Pros: 

• The tested product is very consistent because the integration testing is basically performed in an environment that almost similar to that of reality.
• Stubs can be written with lesser time because when compared to the drivers then Stubs are simpler to author.

Cons: 

• Basic functionality is tested at the end of cycle.
• If core logic is embedded in the lower-level units, it cannot be tested in the first place until the examination of other units finishes. 

Bottom-up Integration Testing

Pros: 

• Can be applied at the early stages, since the examination of the critical functionality starts with the low-level units. 
• If a particular unit stops functioning, a team can fix an error right away.
• Minimal identification and troubleshooting time is required. 

Cons: 

• If the software consists of many small low-level units

that are very difficult to implement, it may take longer
to complete the testing process.

Sandwich Integration Testing

• Sandwich integration testing is a combination of both top down and bottom up approaches. It is also called as hybrid integration testing or mixed integration testing.
• In sandwich integration testing, the system is considered to be made up of three layers:
• A layer in the middle which will be the target of testing;
• A layer above the target layer and a layer below the target layer;
• Testing begins from the outer layer and converges at the middle layer.

Advantage: Top and bottom layers can be tested in parallel.
Disadvantage: Extensive testing of the sub-systems is not performed before the integration.