Fix ordering of simultaneous work in test scheduler. (#94)

* Fix ordering of simultaneous work in test scheduler.

* clean up

* clean up

* UInt

Sources/ComposableArchitecture/Scheduling/TestScheduler.swift

@@ -5,9 +5,10 @@ import Foundation
 public final class TestScheduler<SchedulerTimeType, SchedulerOptions>: Scheduler
 where SchedulerTimeType: Strideable, SchedulerTimeType.Stride: SchedulerTimeIntervalConvertible {
 
+  private var lastId: UInt = 0
   public let minimumTolerance: SchedulerTimeType.Stride = .zero
   public private(set) var now: SchedulerTimeType
-  private var scheduled: [(id: UUID, date: SchedulerTimeType, action: () -> Void)] = []
+  private var scheduled: [(id: UInt, date: SchedulerTimeType, action: () -> Void)] = []
 
   /// Creates a test scheduler with the given date.
   ///
@@ -20,11 +21,7 @@ where SchedulerTimeType: Strideable, SchedulerTimeType.Stride: SchedulerTimeInte
   ///
   /// - Parameter stride: A stride.
   public func advance(by stride: SchedulerTimeType.Stride = .zero) {
-    self.scheduled = self.scheduled
-      // NB: Stabilizes sort via offset.
-      .enumerated()
-      .sorted(by: { $0.element.date < $1.element.date || $0.offset < $1.offset })
-      .map { $0.element }
+    self.scheduled.sort { $0.date < $1.date || $0.id < $1.id }
 
     guard
       let nextDate = self.scheduled.first?.date,
@@ -59,17 +56,17 @@ where SchedulerTimeType: Strideable, SchedulerTimeType.Stride: SchedulerTimeInte
     options _: SchedulerOptions?,
     _ action: @escaping () -> Void
   ) -> Cancellable {
+    let id = self.nextId()
 
-    let id = UUID()
-
-    func scheduleAction(_ date: SchedulerTimeType) -> () -> Void {
+    func scheduleAction(for date: SchedulerTimeType) -> () -> Void {
       return { [weak self] in
         action()
-        self?.scheduled.append((id, date, scheduleAction(date.advanced(by: interval))))
+        let nextDate = date.advanced(by: interval)
+        self?.scheduled.append((id, nextDate, scheduleAction(for: nextDate)))
       }
     }
 
-    self.scheduled.append((id, date, scheduleAction(date.advanced(by: interval))))
+    self.scheduled.append((id, date, scheduleAction(for: date)))
 
     return AnyCancellable { [weak self] in
       self?.scheduled.removeAll(where: { $0.id == id })
@@ -82,11 +79,16 @@ where SchedulerTimeType: Strideable, SchedulerTimeType.Stride: SchedulerTimeInte
     options _: SchedulerOptions?,
     _ action: @escaping () -> Void
   ) {
-    self.scheduled.append((UUID(), date, action))
+    self.scheduled.append((self.nextId(), date, action))
   }
 
   public func schedule(options _: SchedulerOptions?, _ action: @escaping () -> Void) {
-    self.scheduled.append((UUID(), self.now, action))
+    self.scheduled.append((self.nextId(), self.now, action))
+  }
+
+  private func nextId() -> UInt {
+    self.lastId += 1
+    return self.lastId
   }
 }
 

Tests/ComposableArchitectureTests/ComposableArchitectureTests.swift

@@ -3,6 +3,8 @@ import ComposableArchitecture
 import XCTest
 
 final class ComposableArchitectureTests: XCTestCase {
+  var cancellables: Set<AnyCancellable> = []
+
   func testScheduling() {
     enum CounterAction: Equatable {
       case incrAndSquareLater
@@ -60,6 +62,24 @@ final class ComposableArchitectureTests: XCTestCase {
     )
   }
 
+  func testSimultaneousWorkOrdering() {
+    let testScheduler = TestScheduler<DispatchQueue.SchedulerTimeType, DispatchQueue.SchedulerOptions>(
+      now: .init(.init(uptimeNanoseconds: 1))
+    )
+
+    var values: [Int] = []
+    testScheduler.schedule(after: testScheduler.now, interval: 1) { values.append(1) }
+      .store(in: &self.cancellables)
+    testScheduler.schedule(after: testScheduler.now, interval: 2) { values.append(42) }
+      .store(in: &self.cancellables)
+
+    XCTAssertEqual(values, [])
+    testScheduler.advance()
+    XCTAssertEqual(values, [1, 42])
+    testScheduler.advance(by: 2)
+    XCTAssertEqual(values, [1, 42, 1, 1, 42])
+  }
+
   func testLongLivingEffects() {
     typealias Environment = (
       startEffect: Effect<Void, Never>,

Tests/ComposableArchitectureTests/TimerTests.swift

@@ -103,8 +103,8 @@ final class TimerTests: XCTestCase {
 
     scheduler.run()
 
-    XCTAssertEqual(count2, 14)
-    XCTAssertEqual(count3, 9)
+    XCTAssertEqual(count2, 15)
+    XCTAssertEqual(count3, 10)
   }
 
   func testTimerCompletion() {