Avoiding Unit Test Failures Due to Improper Ternary Conditions in Templates
When working with modern frontend frameworks like Vue.js or React, it's common to use conditional expressions such as ternary operators within templates to handle dynamic content. However, improper usage of these operators, especially when dealing with object properties, can lead to unit test failures.
In this article, we’ll dive deep into how improper handling of ternary conditions can cause unit test failures and best practices for ensuring stable and robust code.
1. Understanding Ternary Conditions and Unit Test Failures
What is a Ternary Operator?
A ternary operator in JavaScript is a shorthand for if-else conditions. The syntax is as follows:
In templates, it's often used to conditionally display or process data based on certain conditions. For example:
The problem arises when the object selectedSubscription itself might be null or undefined. If you directly access selectedSubscription.paymentStatus without checking whether selectedSubscription exists, the application will throw a runtime error, causing both the application and unit tests to fail.
Common Scenario Leading to Test Failures:
First we think the error occurred due to Props value is not passing to the script. Then, Even though the prop value was passed, it showed an unrelated error in the comment line in the file script part due to a missing ternary condition in the template.
In frameworks like Vue.js, object properties are often bound to template expressions. Unit test failures related to improper ternary conditions typically occur because the test cases don’t always initialize these objects or they simulate edge cases where objects are null. For example:
If selectedSubscription is undefined, this results in an error like:
This error will cause the entire unit test to fail. To avoid this, we need to ensure the object’s existence using a ternary condition or other validation techniques.
2. Solving Error By If- else:
We can also solve the Unit testing error using v-if and v-else in the templates but it will consume more lines of code comparing to the ternary operator. So the best practices is to go with Ternary operator.
2.1 By means of following ternary procedures, we can avoid the Unit testing error:
In this example, the code checks if selectedSubscription exists before trying to access paymentStatus. If it does not exist, it safely returns "N/A".
2.2 Example using complex template logic :
In this case, if selectedSubscription or selectedSubscription.plan is not null, the code will attempt to access selectedSubscription.plan.name name property in that way we have to write the code. So first of all we have to make sure selectedSubscription or selectedSubscription.plan if any one of the value is null we just have to return empty string or we can return any string that we want.
2.3. Shorthand Property for Ternary Conditions
The ?. operator (optional chaining) checks if selectedSubscription exists before trying to access paymentStatus.
This approach simplifies the code by eliminating the need for a full ternary expression and reduces the risk of encountering undefined errors.
Conclusion: How to Handle Conditional Logic
Equally important is properly handling conditional logic in modern JavaScript frameworks. Common errors, like failing to check object existence before accessing properties, can lead to unit test failures. Adopting best practices such as using ternary conditions correctly, and using optional chaining (?.), in unit tests will result in more reliable code and smoother test execution.
By handling conditional logic carefully, teams can minimize errors, avoid costly rework, and deliver high-quality software that meets stakeholder expectations.