What is Module Testing? (Definition, Examples)

A software application contains an integration of various modules. Modules are programs written in a specific language consisting of subprograms, subroutines, functions, classes, and procedures. Module testing is a process where you need to test each unit of these modules to ensure they adhered to the best coding standards. Unless a module passes the testing phase, it cannot go for the application testing process.

Module testing, aka component testing, helps to early detection of errors in application testing. This can be a massive relief for testers during the later stage of testing. Module testing is a gateway to parallel testing that allows testers to test multiple modules simultaneously.

Why is module testing an essential part of software testing?

Testers prefer module testing for the following reasons −

  • Less time consumption − it is better to divide the application into small parts, aka subprogram or small code units. Instead of handling everything, developers can create unit test cases and assign them to different testers.

  • Supports parallel testing − It allows testing multiple modules independently from a single application. Since modules are smaller in size, testers can pay more attention to them, resulting in a better end product.

  • Reduces Complexity − Testing the complete application at one go can be a complex and tedious affair. In module testing, you can break down an extensive application into small parts or unit levels, reducing the complexity of testing an application as a whole.

Module testing best practices

Some crucial module testing tips for a successful testing process −

Designing the test is the first thing to do before conducting a module test. For preparing the test case, you must consider two essential factors- module specification and source code under test.

It is imperative to analyze the code logic for the module under test. You can do that by using multiple white box methods. You can further expand these test cases by applying black-box techniques.

After designing the test cases, the next step is to associate the modules for testing. You can use an incremental or non-incremental approach to do that.

Suppose you choose the incremental method through the top-down or bottom-up approach. In the top-down approach, you need to test the higher-level modules and gradually moves toward lower ones. Meanwhile, the bottom-up approach is the exact opposite of the top-down module testing.

For the incremental approach, you have to test all modules separately and then integrate them into a whole program later.

You need to prepare test data and supply it to the module via a driver for executing the test. The next step is to monitor the test and store the results.

Module Testing test strategy

Module or component test is conducted by dividing the process into two parts- Component testing in small (CTIS) and component testing in large (CTIL).

Component Testing in Small is a process performed in complete isolation without integrating one component with other.

IMeanwhile, Component Testing in Large is a test process executed without isolating components from each other. Generally, when one component is dependent on the other and isolating them may lead to functionality issues.

In the absence of the dependent component, you can use a dummy object as an alternative. These dummy objects are known as a stub (called function) and driver (calling function).

Integration vs Module Testing

Integration testing − In integration testing, testers combine two components in a sequence and test the system together. The motive is to check the combination of different units and how they interact with each other. It also involves the process to evaluate the way subsystems integrate into a single system.

Assume you are checking the login and sign up features of an ecommerce application. You can consider both logins and sign up as separate units.

Now let’s say you add some items to the basket and move towards checkout. However, before checkout, you have to log inside the app or sign up if you are a new user. Now, you may lose all your items from the basket after the login. So the work of the integration testing is to check the integration between these two functionalities above.

Module testing − In module testing, a single component is tested and later integrated with other components. Based on the previous example, in module testing, you can independently test the signup, sign in, adding items to the cart, etc., and integrate them into a complete application.

In short, we can say that the integration test is the next step of module testing.

What are stubs and drivers?

Drivers are dummy programs used in the absence of a calling function to call the functions of the lowest module.

Stubs are code or snippet that accepts inputs or requests from the top module and responds them successfully.

Module test simplified with an example

Let’s consider an organization is developing a large web application. As an agile tester, you have to complete the testing process faster to launch in the market sooner. Therefore, you cannot wait for months for the app to develop ultimately. So, you need to test the login page as soon as it gets developed. You must execute all test cases ensuring all functionalities of the login page is working as expected.

You can divide the testing process into different sections −

Test the user interface for spelling mistakes, alignment, formatting, logos, etc.

Use negative testing techniques such as authentication and authorization. It is an ideal step to find defects in an early stage.

Test the security features of the page using techniques like SQL injections.

Once you log all the defects, you can pass them on to the development team to make necessary changes for the upcoming pages.

Now, as stated earlier, you only have the login page to test as other pages are yet to be developed. For example, what will happen if you enter your login credentials and hit enter. You don’t have the necessary component for validating the functionality of the login page.

This may be solved if you have a single page stating “login successful” when you enter the correct credential and “Wrong username/password” for wrong credentials. Stubs are used to solve this problem.


Module testing remains a significant part of the testing cycle and a predecessor of integration testing. As it supports parallel testing, it helps speed up the overall testing process, which is extremely important in this agile era. Plus, it also helps in the early detection of errors, allowing you to rectify your mistakes beforehand and minimizes overall test efforts for the testing team.