weak variable is becoming nil while writing testcase?

Question

Hi I am writing a testcase for a function in ViewModel in where I am using a weak variable,

While testing the function , the weak variable is becoming nil , also I instantiated it and provided value to that object just before calling the testing function. Why is it becoming nil , and then how do i test it!!!

ALSO I cannot make weak variable strong type!!, working on others code

Compiler Warning - Instance will be immediately deallocated because property 'source' is 'weak'

CODE

func testFundTrip() {
     viewModel.source = SourceViewTypeMock()
     viewModel.fundTrip(trip)
}

In ViewModel

func fundTrip(_ trip: TravelTrip) {
        if let source = source { 
          // Here source is becoming nil ?? why 
        }
    }

Is there something with testcases methods with scopes of variables ?

Answer 1

The warning is telling you exactly what's happening. You only have a weak pointer to a value, so nothing is going to keep your SourceViewTypeMock alive past the assignment statement. The solution is to create a strong reference. You need one that the compiler is not allowed to optimized out, so it has to be outside of this function. So you make it a property of the test case.

If it's immutable, you can do it this way:

class TheTestCase: XCTestCase {
    let sourceMock = SourceViewTypeMock()

    func testFundTrip() {
        viewModel.source = sourceMock
        viewModel.fundTrip(trip)
    }
}

If it's mutable, then you probably want to make sure you recreate it in setUp:

class TheTestCase: XCTestCase {
    var sourceMock: SourceViewTypeMock!

    override func setUp() {
        sourceMock = SourceViewTypeMock()
    }

    func testFundTrip() {
        viewModel.source = sourceMock
        viewModel.fundTrip(trip)
    }
}