Files
fuelboard/FuelBoardTests/Tests/FuelBoardSharedTests/FuelSavingsEstimateTests.swift
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FuelBoard Contributor d7a0ecb79a Add Worth the Drive fuel savings with road-routed estimates
Optional Fuel Savings feature (off by default): vehicle MPG in UK imperial gallons, fill amount in pounds or litres, persisted through the existing keychain/app-group store. Ranks the WHOLE station pool by estimated net saving (fuel-price saving at each pump minus the extra return-trip driving cost) using MapKit road distances with a straight-line fallback marked (est.).

The closest station with a valid price for the selected fuel is the comparison baseline and is labelled "Closest station"; other rows read "Save £X.XX after travel" / "£X.XX worse off after travel" / "Break even". Labels live in the shared model so they are unit-tested. The TOP badge still marks the cheapest pump price and reads "CHEAPEST" when the list is ranked by net saving.

Road routing now prioritises the Worth-the-Drive candidates plus the baseline and merges cache entries instead of replacing them, so far-out stations get real routes rather than permanent straight-line estimates. Numeric fields gain a Done button above the keypad (decimalPad has no Return key); the fill-up control is hidden unless the feature is configured; Favourites shares one session fill amount with the station list. 131 tests.
2026-10-11 14:34:53 +01:00

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import XCTest
#if SWIFT_PACKAGE
@testable import FuelBoardShared
#endif
/// Ranking rules for the Worth the Drive sort.
///
/// Regression: the sort used to rank only a shortlist of the nearest stations
/// whose ROAD ROUTES had been measured, and everything else was listed as
/// unavailable. Cheaper stations a few miles further out — the exact stations
/// the sort exists to surface — were dropped from the top of the list, and
/// stations on later pages showed no savings at all.
final class FuelSavingsEstimateTests: XCTestCase {
private let settings = FuelSavingsSettings(
enabled: true,
mpg: 45,
preferredAmount: FuelSavingsFillAmount(value: 40, unit: .pounds)
)
private let amount = FuelSavingsFillAmount(value: 40, unit: .pounds)
private func station(_ id: String,
price: Double?,
lat: Double = 51.5,
lng: Double = -0.1) -> FuelStation {
FuelStation(
id: id,
name: id,
brand: "X",
address: "",
postcode: "",
lat: lat,
lng: lng,
prices: price.map { [FuelType.e10: $0] } ?? [:],
priceUpdated: nil
)
}
/// Straight-line out-and-back estimate, as the app builds it when no road
/// route has been measured yet.
private func straightLine(_ miles: Double) -> FuelSavingsJourney {
FuelSavingsJourney(miles: miles, basis: .straightLine)
}
func testCheaperStationThreePointFiveMilesAwayIsRankedFirstWithASaving() {
// Nearest station: 1 mile away at 145.9p. The station the user can see
// in the Cheapest tab: 3.5 miles away at 138.9p.
let baseline = station("baseline", price: 145.9)
let candidate = station("cheaper-3.5", price: 138.9, lat: 51.55)
let filler = (0..<14).map { station("filler-\($0)", price: 150 + Double($0)) }
let pool = [baseline, candidate] + filler
let ranked = FuelSavingsEstimator.ranked(
pool,
fuel: .e10,
baseline: baseline,
settings: settings,
amount: amount,
journeyMiles: { s in
switch s.id {
case "baseline": return self.straightLine(2.0)
case "cheaper-3.5": return self.straightLine(7.0)
default: return self.straightLine(20.0)
}
}
)
XCTAssertEqual(ranked.count, pool.count)
XCTAssertEqual(ranked.first?.id, "cheaper-3.5",
"a cheaper station 3.5 miles away must rank above the nearest station")
let result = FuelSavingsEstimator.availability(
station: candidate,
fuel: .e10,
baseline: baseline,
settings: settings,
amount: amount,
journey: straightLine(7.0),
baselineJourney: straightLine(2.0)
)?.result
XCTAssertNotNil(result, "the station must show a saving, not an unavailable state")
XCTAssertGreaterThan(result?.netSavingGBP ?? -1, 0)
XCTAssertEqual(result?.status, .worthTheDrive)
XCTAssertEqual(result?.distanceBasis, .straightLine,
"unmeasured routes are reported as straight-line estimates")
}
func testEveryPricedStationInThePoolIsEstimatedNotJustAShortlist() {
// 40 stations, but only the first one has a measured road route — the
// old implementation capped the whole ranking to 12 shortlisted
// stations and returned "Outside route shortlist" for the rest.
let baseline = station("baseline", price: 145.9)
let pool = [baseline] + (0..<39).map { station("s\($0)", price: 135 + Double($0)) }
let ranked = FuelSavingsEstimator.ranked(
pool,
fuel: .e10,
baseline: baseline,
settings: settings,
amount: amount,
journeyMiles: { s in
s.id == "baseline"
? FuelSavingsJourney(miles: 2.0, basis: .roadRoute)
: self.straightLine(2.0 + (Double(s.id.dropFirst()) ?? 6))
}
)
XCTAssertEqual(ranked.count, pool.count)
for station in pool where station.id != "baseline" {
let availability = FuelSavingsEstimator.availability(
station: station,
fuel: .e10,
baseline: baseline,
settings: settings,
amount: amount,
journey: straightLine(10.0),
baselineJourney: FuelSavingsJourney(miles: 2.0, basis: .roadRoute)
)
XCTAssertNotNil(availability?.result,
"\(station.id) should carry an estimated saving, not an unavailable state")
}
}
func testMeasuredRoadRoutesAreReportedAsRoadRouteBasis() {
let baseline = station("baseline", price: 145.9)
let candidate = station("candidate", price: 138.9)
let result = FuelSavingsEstimator.availability(
station: candidate,
fuel: .e10,
baseline: baseline,
settings: settings,
amount: amount,
journey: FuelSavingsJourney(miles: 7.0, basis: .roadRoute),
baselineJourney: FuelSavingsJourney(miles: 2.0, basis: .roadRoute)
)?.result
XCTAssertEqual(result?.distanceBasis, .roadRoute)
XCTAssertFalse(FuelSavingsDistanceBasis.roadRoute.isEstimate)
}
func testMixedBasisIsReportedAsAnEstimate() {
let baseline = station("baseline", price: 145.9)
let candidate = station("candidate", price: 138.9)
// Baseline measured, candidate not: the comparison is only as good as
// its weakest leg, so it must be labelled an estimate.
let result = FuelSavingsEstimator.availability(
station: candidate,
fuel: .e10,
baseline: baseline,
settings: settings,
amount: amount,
journey: straightLine(7.0),
baselineJourney: FuelSavingsJourney(miles: 2.0, basis: .roadRoute)
)?.result
XCTAssertEqual(result?.distanceBasis, .straightLine)
}
func testStationWithoutAPriceIsUnavailable() {
let baseline = station("baseline", price: 145.9)
let noPrice = station("no-price", price: nil)
let availability = FuelSavingsEstimator.availability(
station: noPrice,
fuel: .e10,
baseline: baseline,
settings: settings,
amount: amount,
journey: straightLine(4.0),
baselineJourney: straightLine(2.0)
)
XCTAssertEqual(availability, .unavailable("No price"))
}
func testFeatureOffProducesNoSavingsRow() {
let baseline = station("baseline", price: 145.9)
let candidate = station("candidate", price: 138.9)
let availability = FuelSavingsEstimator.availability(
station: candidate,
fuel: .e10,
baseline: baseline,
settings: .defaults,
amount: amount,
journey: straightLine(4.0),
baselineJourney: straightLine(2.0)
)
XCTAssertNil(availability)
}
// MARK: - Required wording and baseline labelling
private var briefSettings: FuelSavingsSettings {
FuelSavingsSettings(enabled: true,
mpg: 30,
preferredAmount: FuelSavingsFillAmount(value: 60, unit: .pounds))
}
private var briefAmount: FuelSavingsFillAmount {
FuelSavingsFillAmount(value: 60, unit: .pounds)
}
/// The scenario from the brief: 30 MPG, £60 fill, baseline Rontec Shelf
/// (171.9p, 0.4 mi), candidate Shell Whetley Hill (167.9p, 3.8 mi).
///
/// Whetley Hill is 4p/litre cheaper, yet it is WORSE OFF — and that is
/// correct, not a calculation bug: £60 buys 34.90 L at 171.9p, so the
/// cheaper pump saves 34.90 × 4p = £1.40, while the extra 6.8 return miles
/// burn 6.8/30 × 4.54609 = 1.03 L at 167.9p = £1.73. Net ≈ −£0.33.
func testCheaperStationFurtherAwayIsWorseOffAfterTravel() {
let baseline = station("rontec-shelf", price: 171.9)
let candidate = station("shell-whetley-hill", price: 167.9)
let availability = FuelSavingsEstimator.availability(
station: candidate,
fuel: .e10,
baseline: baseline,
settings: briefSettings,
amount: briefAmount,
journey: straightLine(7.6), // 3.8 mi out and back
baselineJourney: straightLine(0.8) // 0.4 mi out and back
)
guard let result = availability?.result else {
return XCTFail("expected an estimate, got \(String(describing: availability))")
}
XCTAssertEqual(result.fillLitres, 34.904, accuracy: 0.005,
"the £60 budget buys litres at the BASELINE pump price")
XCTAssertEqual(result.grossSavingGBP, 1.396, accuracy: 0.005)
XCTAssertEqual(result.extraDistanceMiles, 6.8, accuracy: 0.001,
"only the return-trip DELTA counts — the shared journey is never counted twice")
XCTAssertEqual(result.extraDrivingCostGBP, 1.730, accuracy: 0.005)
XCTAssertEqual(result.netSavingGBP, -0.334, accuracy: 0.005)
XCTAssertEqual(result.status, .notWorthTheDrive)
XCTAssertEqual(result.headline(compact: true), "£0.33 worse off after travel (est.)")
}
func testMeasuredRoadRoutesDropTheEstimateMarker() {
let baseline = station("baseline", price: 171.9)
let candidate = station("candidate", price: 167.9)
let availability = FuelSavingsEstimator.availability(
station: candidate,
fuel: .e10,
baseline: baseline,
settings: briefSettings,
amount: briefAmount,
journey: FuelSavingsJourney(miles: 7.6, basis: .roadRoute),
baselineJourney: FuelSavingsJourney(miles: 0.8, basis: .roadRoute)
)
XCTAssertEqual(availability?.result?.distanceBasis, .roadRoute)
XCTAssertEqual(availability?.result?.headline(compact: true), "£0.33 worse off after travel")
XCTAssertEqual(availability?.result?.headline(), "£0.33 worse off after travel")
}
func testBaselineRowIsLabelledClosestStation() {
let baseline = station("nearest", price: 171.9)
let availability = FuelSavingsEstimator.availability(
station: baseline,
fuel: .e10,
baseline: baseline,
settings: briefSettings,
amount: briefAmount,
journey: straightLine(0.8),
baselineJourney: straightLine(0.8)
)
XCTAssertEqual(availability?.result?.status, .baseline)
XCTAssertEqual(availability?.result?.headline(compact: true), "Closest station")
XCTAssertEqual(FuelSavingsStatus.baseline.displayName, "Closest station")
XCTAssertEqual(availability?.result?.netSavingGBP, 0)
XCTAssertEqual(availability?.result?.extraDistanceMiles, 0)
}
func testPositiveResultHeadlineSaysSaveAfterTravel() {
// 4p cheaper AND almost the same distance, so the saving survives travel.
let baseline = station("baseline", price: 160.0)
let candidate = station("candidate", price: 150.0)
let availability = FuelSavingsEstimator.availability(
station: candidate,
fuel: .e10,
baseline: baseline,
settings: briefSettings,
amount: briefAmount,
journey: straightLine(6.4),
baselineJourney: straightLine(6.0)
)
guard let result = availability?.result else {
return XCTFail("expected an estimate, got \(String(describing: availability))")
}
XCTAssertEqual(result.status, .worthTheDrive)
// £60 buys 37.5 L at 160p; 10p/litre cheaper saves £3.75; 0.4 extra
// return miles cost ~£0.09. Net ≈ £3.66.
XCTAssertEqual(result.netSavingGBP, 3.659, accuracy: 0.005)
XCTAssertEqual(result.headline(compact: true), "Save £3.66 after travel (est.)")
}
func testNeutralResultHeadlineIsBreakEven() {
// 0.1p cheaper over the same distance: inside the break-even tolerance.
let baseline = station("baseline", price: 150.0)
let candidate = station("candidate", price: 149.9)
let availability = FuelSavingsEstimator.availability(
station: candidate,
fuel: .e10,
baseline: baseline,
settings: briefSettings,
amount: briefAmount,
journey: straightLine(6.0),
baselineJourney: straightLine(6.0)
)
XCTAssertEqual(availability?.result?.status, .breakEven)
XCTAssertEqual(availability?.result?.headline(compact: true), "Break even")
XCTAssertEqual(availability?.result?.headline(), "Break even")
}
/// The exact strings the brief asks for.
func testHeadlineWordingMatchesTheBrief() {
XCTAssertEqual(FuelSavingsResult.baselineHeadline, "Closest station")
XCTAssertEqual(FuelSavingsResult.breakEvenHeadline, "Break even")
let saving = FuelSavingsResult(fillLitres: 34.9,
grossSavingGBP: 1.40,
extraDrivingCostGBP: 0.88,
extraDistanceMiles: 3.5,
netSavingGBP: 0.52,
status: .worthTheDrive,
distanceBasis: .roadRoute)
XCTAssertEqual(saving.headline(), "Save £0.52 after travel")
let loss = FuelSavingsResult(fillLitres: 34.9,
grossSavingGBP: 1.40,
extraDrivingCostGBP: 1.71,
extraDistanceMiles: 6.8,
netSavingGBP: -0.31,
status: .notWorthTheDrive,
distanceBasis: .roadRoute)
XCTAssertEqual(loss.headline(), "£0.31 worse off after travel")
}
/// The sort must order by NET saving, not pump price: a pricier station can
/// win when the cheaper one is far enough away.
func testSortingRanksByNetSavingNotPumpPrice() {
let baseline = station("baseline", price: 171.9)
let cheapButFar = station("cheap-but-far", price: 167.9)
let pricierButNear = station("pricier-but-near", price: 169.9)
let ranked = FuelSavingsEstimator.ranked(
[baseline, cheapButFar, pricierButNear],
fuel: .e10,
baseline: baseline,
settings: briefSettings,
amount: briefAmount,
journeyMiles: { s in
switch s.id {
case "baseline": return self.straightLine(0.8)
case "cheap-but-far": return self.straightLine(7.6)
default: return self.straightLine(1.2)
}
}
)
XCTAssertEqual(ranked.first?.id, "pricier-but-near",
"net saving decides the order, not the pump price")
XCTAssertEqual(ranked.last?.id, "cheap-but-far")
}
}