Though these two have several differences with regards to approach, testing strategy, performance, etc. the ultimate concept of these two methods for delivering a quality-assured application or software.


Applications or the software that are developed are either written in code that is of higher or lower-level language; this difference in the modules helps in classifying the testing methods like unit testing and sandwich testing.Testing is one of the crucial stages in every application or software development lifecycle (SDLC). For the present businesses, deliverables with quality assurance is an important strategy. And, every enterprise is aiming to achieve this effect by adopting the right testing methodologies.

Unit testing and Sandwich testing (Hybrid Testing) are two important approaches that are considered by testing teams to validate an application. These two testing methods are having the specific features that make them efficient; below find the differences between these two approaches so that enterprises can easily leverage them.

Differences between Unit Testing and Sandwich Testing


Unit testing is the method that is practised as the first level of testing before integration testing in the Software Testing Lifecycle (STLC), SDLC, and V Model. In this method, a software component or a single module is tested at a time. This approach helps to check whether each unit of the software is functioning as expected or not.

Whereas in Sandwich Testing, each module is like a separate module for testing. After completing the test, each module gets integrated one by one. Sandwich testing is a combination of two approaches – the bottom-up approach and the top-down approach.

The strategy of the testing approaches:

Unit testing is practised in two methods, i.e. by manual and automated methods with different code coverage techniques such as decision coverage, branch coverage, condition coverage, statement coverage, etc.

In Sandwich testing, there are three important layers known as the Main target layer, the layer that is above the main target layer, and a layer that is below the main target layer. In this approach, testing is more focussed on the main layer, and it selects the testing components based on code structure and system characteristics.

Performance of the testing approaches:

As mentioned above, unit testing can be performed manually and with automated testing methods. While performing this testing approach, the code functions of an application are executed in a test environment, and the achieved output is then compared with the expected output. If the output meets the expected requirement, then the test is considered as a success and if the output fails to match the expectation then this is a failure. Necessary changes and re-testing of the code is performed until the output matches the expected requirement.

Whereas in Sandwich testing, it is performed in three steps. Stubs are used to test the user interface in isolation. Then, the drivers are used to test the lowest level functions. The main target layer is tested only when the complete system gets integrated.

Parallel Testing:

As single modules are subjected to unit testing, there is no scope for parallel testing to be supported by unit testing. Whereas in sandwich testing, parallel testing is supported as it performs with several modules.

Advantages of the Test Approaches:

The benefits of Unit Testing:

  • This approach helps in speeding up the coding process and makes coding agile
  • Bugs are identified and resolved at the earliest and thus, it helps in reducing the testing costs
  • This method simplifies the debugging process as the debugging is done only for the latest changes

The benefits of Sandwich Testing:

  • This approach effectively helps in saving time
  • It helps to provide better coverage with same stubs
  • It helps in performing parallel testing, and the use of various sub-projects influences many large projects to use this approach


There are a number of test automation tools for performing unit testing, a few of the tools are EMMA, JMockit, NUnit, PHPUnit, Junit, etc.

Similarly, there are even a good number of testing tools for performing sandwich testing, and a few of them are Citrus, LDRA, Rational Integration tester by IBM, Tessy, Pioneers, Steam, etc.


Testing the app or the software helps developers to identify the bugs at earliest and assures to provide the opportunity to improve the quality of the application. Unit testing and Sandwich testing are two different testing approaches that are helping to achieve quality-assured applications and software in the SDLC. To be ahead in the present business marketArticle Submission, enterprises need to choose the right testing methodologies or leverage services from expert QA specialists.


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