시뮬레이터엔 펜이 없어

        // UI tests start from the standard settings, whatever earlier runs left behind.
        let environment = ProcessInfo.processInfo.environment
        settings = environment["ARIANDEL_RESET_SETTINGS"] == "1" ? StudioSettings.defaults : StudioSettings.load(from: defaults)
        if environment["ARIANDEL_RESET_SETTINGS"] == "1" { defaults.removeObject(forKey: GenerationSettings.key) }
        // UI tests run on a simulator, which has no Pencil.
        if environment["ARIANDEL_FINGER_PAINTING"] == "1" {
            settings.fingerPainting = true
        }
        // UI tests: a context menu on a draggable row (a brush, an artwork) never tells XCTest
        // its animations ended, and every later step waited 60 s for it; the app sat idle.
        if environment["ARIANDEL_NO_ANIMATIONS"] == "1" {
            UIView.setAnimationsEnabled(false)
        }

    /// Settings a test keeps to itself: nothing it changes reaches the app's own defaults or the next test.
    private func isolatedDefaults() -> UserDefaults {
        let name = "ariandel-tests-\(UUID().uuidString)"
        addTeardownBlock { UserDefaults.standard.removePersistentDomain(forName: name) }
        return UserDefaults(suiteName: name)!
    }

import Foundation

// A minimal sketch: two tests of the same Pencil Pro roll. The first checks the
// Swift side alone, the way a hardware-free unit test can; the second carries the
// value across the boundary through a mirror of the two libmypaint lines that
// consume it (mypaint-brush.c: `barrel_rotation * 360`, then
// smallest_angular_difference from a freshly reset brush state of 0).

// Ariandel's conversion (StylusInput.swift, barrelRotation(for:)): radians -> 0...360 degrees.
func barrelRotation(roll: Double) -> Float {
    var degrees = (roll * 180 / .pi).truncatingRemainder(dividingBy: 360)
    if degrees < 0 { degrees += 360 }
    return Float(degrees)
}

// libmypaint's helpers.c, transcribed.
func modArith(_ a: Float, _ n: Float) -> Float { a - n * (a / n).rounded(.down) }
func smallestAngularDifference(_ a: Float, _ b: Float) -> Float {
    var d = modArith(b - a + 180, 360) - 180
    d += d > 180 ? -360 : d < -180 ? 360 : 0
    return d
}
// What the brush's barrel state becomes for one argument, from a reset state of 0.
func libmypaintBarrel(argument: Float) -> Float { smallestAngularDifference(0, argument * 360) }

let roll = 90 * Double.pi / 180            // a quarter turn of the barrel
let sent = barrelRotation(roll: roll)
print("swift side:  roll 90° -> sends \(sent)   test passes: \(abs(sent - 90) < 1e-3)")
let seen = libmypaintBarrel(argument: sent)
print("across:      libmypaint holds \(seen)°   test passes: \(abs(seen - 90) < 1e-3)")
let fixed = libmypaintBarrel(argument: sent / 360)
print("sent / 360:  libmypaint holds \(fixed)°  test passes: \(abs(fixed - 90) < 1e-3)")

// Prints:
// swift side:  roll 90° -> sends 90.0   test passes: true
// across:      libmypaint holds 0.0°   test passes: false
// sent / 360:  libmypaint holds 90.0°  test passes: true