August 15, 2023

Assertions, also known as verifications, are especially important when testing with machine learning.

Assertions, also known as verifications, are especially important when testing with machine learning.

Assertion is a key concept in functional testing. In essence, assertions are used to declare the expected behavior or outcome of a test. The test fails when the behavior or outcome of the test does not conform with the expectation. Using assertion in testing brings many benefits, including speeding up the testing process and improving accuracy of results

Using assertion-based testing can help testers catch errors immediately. It also has the potential to bring out subtle errors that are otherwise difficult to catch.

What is Assertion?

 At the basic level, an assertion is just a Boolean expression. It contains a true and false binary. The expression is placed into the testing program and pertains to a certain section of the software being tested. The assertion itself encompasses an expression that describes the logic of the code under test. While the test runs without any errors, the assertion remains true. However, with any system error, the assertion becomes false. This is a clear indicator of an error and can be used in a variety of errors to help with testing.

 How is Assertion Used in Functional Testing?

 Assertion is used in functional testing in two ways. Testers can make use of hard or soft assertions, depending on their workflow and how they want the process to work after an error has occurred.

With a hard assertion, any system error that causes the assertion to return a false result will stop the execution. Further steps in the execution will not go forward unless it is manually restarted. On the other hand, a soft assertion means that the execution will keep going forward and proceed through all further steps in the chain, even when the assertion has returned a false result due to an error.

Assertion can be employed in a variety of ways. Here are a few methods.

  • An assertion can have a defined Boolean argument and can be used to verify if a stated condition is either true or false. Depending on the configuration, a failure in the verification can result in an assertion error.
  • An assertion can be built using two string arguments. It then checks whether the two arguments are equal during the course of the execution and throw up an error if they are not. This can also be run using three string arguments where the third is a message that comes up if an error occurs. This is useful for more verbose and descriptive assertion testing.
  • An assertion can be built using two Boolean arguments. It then checks whether the two arguments are equal during execution and throws up an error if they are not.
  • An assertion can be built using two Java collection objects. It then checks if both collections contain the same elements, in the same correct order. Any mismatch or problems with the order can throw up an error. This can also be passed with a string message which is displayed when the error occurs.

Benefits of Assertion Testing

 Using assertion in functional testing has certain distinct advantages. Here are a few important ones to consider.

  • With assertion testing, it is possible to detect even small and subtle errors, many of which may escape detection when using other techniques of testing and error detection.
  • Especially with hard assertions, it is possible for testers to detect errors as soon as they occur. As the execution stops immediately after an error is detected, testers can expedite fixing the error before going forward with the rest of the test.
  • Assertions can also help testers make decisions of specific parts of the code which are guaranteed to return specific, error-free results.

Limitations and Pitfalls


While assertion testing is a great way to avoid errors, there are certain limitations and pitfalls that need careful handling.

  • While assertions are effective at pointing out if an error has occurred, using assertions does not provide any guidance regarding the nature and details of the error.
  • Using assertions can sometimes have unintended consequences on the rest of your testing procedure. It can also miss certain bugs and at other times result in false positives.
  • Assertion testing is not an ideal testing method for all kinds of test conditions. It is more useful for testing conceptual test conditions rather than practical ones.
  • Assertion testing can be time-consuming, especially if there are multiple errors in a test. Since hard assertions stop the execution each time an error occurs, this can result in increased time per test.
  • Designing high-quality assertions requires a certain degree of skill and experience.

Results Matter

This clearly demonstrates the myriad advantages of assertions in functional testing and how it can be put to good use for multiple use cases. While there are certain pitfalls to be wary about, these pitfalls can be overcome using a modern solution like Functionize Architect, which allows you to create tests with standard assertions or use advanced options or custom code to further customize validations to yield the desired results.

Assertions, also known as verifications, are especially important when testing with machine learning. One of the key benefits of machine learning based testing is that tests autonomously heal to ensure that they don’t break when the UI of the application under test is changed. This means that the test is dynamically changing on its own. You should make sure to add assertions throughout your test to ensure that the core workflow of the test remains as intended. These verification steps serve as “checkpoints” to ensure that the expected behavior is observed. For example: after clicking on the “Pay Now” button, you expect to see that the Shopping Cart page is loaded so that you can confirm the payment details.

About the author

author photo: Tamas Cser

Tamas Cser


Tamas Cser is the founder, CTO, and Chief Evangelist at Functionize, the leading provider of AI-powered test automation. With over 15 years in the software industry, he launched Functionize after experiencing the painstaking bottlenecks with software testing at his previous consulting company. Tamas is a former child violin prodigy turned AI-powered software testing guru. He grew up under a communist regime in Hungary, and after studying the violin at the University for Music and Performing Arts in Vienna, toured the world playing violin. He was bitten by the tech bug and decided to shift his talents to coding, eventually starting a consulting company before Functionize. Tamas and his family live in the San Francisco Bay Area.

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