The error message “cannot use spyOn on a primitive value; undefined given” is a common error that occurs when trying to use the spyOn function from a testing framework, such as Jasmine or Jest, on a primitive value.
The spyOn function is typically used to create a spy object that simulates the behavior of a real object or function, allowing you to track method calls and return values during testing. However, it can only be used on objects or functions, not on primitive values like numbers, strings, or booleans.
Here is an example to illustrate the error:
const value = 10;
spyOn(value, 'toString'); // Error: cannot use spyOn on a primitive value; undefined given
In this example, we are trying to spy on the toString method of a number, which is a primitive value. This will result in the error message mentioned above.
To resolve this issue, you should ensure that you are trying to spy on an object or a function, rather than a primitive value. For example, if you have a function that returns a number, you can spy on that function instead:
function getValue() {
return 10;
}
spyOn(getValue, 'toString'); // This will work
In this case, we are spying on the getValue function instead of the primitive value itself.
It is important to note that spyOn can only be used on objects or functions that have been defined and are accessible in your test environment. If you are trying to spy on a value that is not defined or is undefined, you may need to modify your test setup or mock the value using other techniques provided by your testing framework.
Overall, the error “cannot use spyOn on a primitive value; undefined given” occurs when trying to use the spyOn function on a primitive value instead of an object or a function. To resolve this issue, make sure you are trying to spy on the correct entity and that it is accessible in your test environment.