An extension to Combine's Publisher that adds a function `expectChange` that takes a predicate and returns an expectation that is fulfilled whenever that predicate evaluates true

Publisher+XCTestExpectation.swift

import XCTest
import Combine

@available(macOS 10.15, iOS 13.0, tvOS 13.0, watchOS 6.0, *)
extension Publisher where Self.Failure == Never {
    func expectChange(where predicate: ((Self.Output) -> Bool)? = nil, timeout: Int = 5) -> XCTestExpectation {
        let expectation = XCTestExpectation(description: "something changed")

        let cancellable = self.sink { value in
            guard let predicate else {
                
                expectation.fulfill()
                return
            }

            if predicate(value) {
                
                expectation.fulfill()
            }
        }

        // This is needed because the sink's Cancellable ref needs to be hold in order for it to not be deallocated.
        // Handling it here allows the caller of this function to be free of handling it.
        DispatchQueue.main.asyncAfter(deadline: .now() + .seconds(timeout)) {
            cancellable.cancel()
        }

        return expectation
    }
}