MuleSoft TDD with the use of MUnit

Testing unit code has always been essential to software engineering since it makes sure that any bugs within the code are identified and rectified before they become a problem in production.

With the introduction and implementation of the Agile framework, Unit testing has been transformed drastically due to test-driven development (TDD) method.

TDD is a software development technique where unit tests are utilized to help drive the development process. In this blog post, I’ll explain how to use TDD and provide some suggestions on how to write amazing test cases using the MUnit tool.

Benefits of Testing-Driven Development

There are numerous benefits to the TDD method. The most obvious benefits are fewer defects and improved code quality. These are achieved when the code is less and simpler. This is exactly how code is written in the process of TDD.

A well-structured and simple-looking code is also simpler to understand and comprehend and improves its reliability of it.

Another advantage that might not be evident is the establishment of an automated testing suite for regressions. It reduces the chance of creating bugs due to small changes to the code. Unit tests are an important component of the build lifecycle to ensure that developers do not break other features.

They spot the issue before they deploy your new software. It is not surprising that TDD is generally preferred whenever CI/CD (i.e. Continuous Integration and continual development) is part of the picture.

However, not everything can be ideal when using TDD. Implementing TDD will require more development time, and could increase the cost of maintenance if implemented in a proper manner. Any bugs discovered in production need to be corrected by separating the actual code as well as a unit test.

How do you use TDD in MuleSoft projects?

As always with MuleSoft begin by creating a product for your ideas and listing the preferred features. After that, you can identify the APIs in the application network and explain the features’ functionality.

To further dissect the APIs, I would suggest following an algorithm called the VETRO Pattern (Validate Enrich, Transform, Validate Operate, and Route) that breaks down the primary APIs’ functions. Therefore, the following step would be to design a Mule subflow that handles each of the functions listed above, if they are applicable. Join a MuleSoft certification course today and become certified.

With the fundamental setup established, you are able to begin a bottom-up, testing-driven development phase that will go through different variations of the same basic steps:

Create a test for one of the sub-flows. Then, declare the desired result.

Code is the easiest way to pass the test.

Test the test and confirm that it is passed.

Refactor the code in accordance with acceptable standards.

Repeat with the next subflow.

If all sub-flows are implemented and tested correctly then write a test for the main flow, and follow the same procedure.

The concept behind this technique is that, in the end, the primary flow doesn’t just include the functions of its sub-flows, but also includes the functionality you want from the API. It’s a good thing that it’s already unit-tested!

Tips on how to write efficient MUnit Tests

Below, you’ll discover some tips for making MUnit tests that are successful as well as some examples.

Do one test at one time

It’s impossible to write separate tests to test the Mule processor! A unit test covering a (sub) flow is able to isolate and test a significant section of code with a reasonable amount of effort.

Expect similar results.

However many tests you run through MUnit test, no matter how many times you run the MUnit test will give the same result as long as the test’s code and the test have not changed. Check out these MuleSoft training videos to learn more.

Do not assert any fixed value since their values can change depending on the environment. Instead, confirming that the variables aren’t null is enough to prove that the code is working.

Make a mock-up of all calls both internal and externe

External calls must be mocked since they do not fall as part of unit testing. We recommend that all calls be mocked in order to ensure that there are no overlaps in multiple tests.

Repeat the test case. Once 3 of your sub-flows are developed and tested, start creating the principal flow. Since all the sub-flows have been tested they can be mocked out and then focus on testing the other message processing systems. In this example, we test the final output to the flow’s main one.

Check the scenarios for errors too.

Many developers focus on the happy ones and leave out the “rainy-day scenarios’ even considering they are equally crucial. In the ideal scenario, there should be enough tests to demonstrate every possible outcome.

We are testing our program’s behavior in case the external endpoint is returned with the HTTP Code 401 (Unauthorized).

Don’t test your knowledge in a way that is dependent on one other.

This makes tests difficult to maintain and debug. There should never be a presumption or expectation for your unit test run in any particular sequence.

Make use of a naming convention.

Give a memorable and friendly name for each MUnit test as well as connect the names to the function of the test tests.


In the end, TDD with the use of MUnit is a great method of identifying flaws early in development. If it is done correctly it will enhance the quality of code, decrease the complexity of code, eliminate regression errors and permit safe refactoring of the code.

With a solid and established method of TDD the development team can provide high-quality products to both the business and all its customers.

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