[Woo POS] Unit tests for TotalsViewModel

[iamgabrielma]

From the refactor on #13211 (comment) we can now test the expected functionality of this bit. A starter list can be found in TotalsViewModelTests:

    func test_isSyncingOrder() {}
    func test_startSyncOrder() {}
    func test_stopSyncOrder() {}
    func test_order() {}
    func test_formattedPrice() {}
    func test_formattedOrderTotalPrice() {}
    func test_formattedOrderTotalTaxPrice() {}
    func test_areAmountsFullyCalculated() {}
    func test_clearOrder() {}
    func test_setOrder() {}

[dangermattic]

Thanks for reporting! 👍