Writing unit tests in the presence of a module init function in Ballerina

I have a package like the following:

FooClient ep;

function init() returns error? {
    do {
        ep = check new ("https://some-api", "id", "secret");
        // do some more stuff
    } on fail var e {
        // log error
        return e;
    }
}

function funcToBeTested() returns anydata {
    return "foo";
}

When initialising the FooClient instance, it'll make a network call to retrieve a token to be used by the client. I also have functions such as funcToBeTested which are modular pieces of logic that I want to test by writing unit tests. However running these unit tests is an issue because when the tests run, the module init function runs too. Which means I have to provide proper credentials for some-api even when running the unit tests. But I don't want to do that since the functionalities I do want to test have no relation to that client initialisation. Is there a way around this?

We can make use of function mocking to get around this.

We can introduce a function to initialise the fooClient and then mock that function using function mocking to return a mock client instead of the original client. You can refer to the test guide at https://ballerina.io/learn/test-ballerina-code/test-services-and-clients/#mock-final-clients for further details.