TunnelMonitor: add initial connection test

8 files changed, 403 insertions, 2 deletions

diff --git a/ios/MullvadVPN.xcodeproj/project.pbxproj b/ios/MullvadVPN.xcodeproj/project.pbxproj
index c8b8755373..f905c92b0c 100644
--- a/ios/MullvadVPN.xcodeproj/project.pbxproj
+++ b/ios/MullvadVPN.xcodeproj/project.pbxproj
@@ -68,6 +68,7 @@
 		580810E82A30E15500B74552 /* DeviceCheckRemoteServiceProtocol.swift in Sources */ = {isa = PBXBuildFile; fileRef = 580810E72A30E15500B74552 /* DeviceCheckRemoteServiceProtocol.swift */; };
 		580810E92A30E17300B74552 /* DeviceCheckRemoteServiceProtocol.swift in Sources */ = {isa = PBXBuildFile; fileRef = 580810E72A30E15500B74552 /* DeviceCheckRemoteServiceProtocol.swift */; };
 		580909D32876D09A0078138D /* RevokedDeviceViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = 580909D22876D09A0078138D /* RevokedDeviceViewController.swift */; };
+		58092E542A8B832E00C3CC72 /* TunnelMonitorTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58092E532A8B832E00C3CC72 /* TunnelMonitorTests.swift */; };
 		580F8B8328197881002E0998 /* TunnelSettingsV2.swift in Sources */ = {isa = PBXBuildFile; fileRef = 580F8B8228197881002E0998 /* TunnelSettingsV2.swift */; };
 		580F8B8428197884002E0998 /* TunnelSettingsV2.swift in Sources */ = {isa = PBXBuildFile; fileRef = 580F8B8228197881002E0998 /* TunnelSettingsV2.swift */; };
 		5811DE50239014550011EB53 /* NEVPNStatus+Debug.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5811DE4F239014550011EB53 /* NEVPNStatus+Debug.swift */; };
@@ -78,6 +79,8 @@
 		581DA2732A1E227D0046ED47 /* RESTTypes.swift in Sources */ = {isa = PBXBuildFile; fileRef = 581DA2722A1E227D0046ED47 /* RESTTypes.swift */; };
 		581DA2752A1E283E0046ED47 /* WgKeyRotation.swift in Sources */ = {isa = PBXBuildFile; fileRef = 581DA2742A1E283E0046ED47 /* WgKeyRotation.swift */; };
 		581DA2762A1E2FD10046ED47 /* WgKeyRotation.swift in Sources */ = {isa = PBXBuildFile; fileRef = 581DA2742A1E283E0046ED47 /* WgKeyRotation.swift */; };
+		581F23AD2A8CF92100788AB6 /* MockDefaultPathObserver.swift in Sources */ = {isa = PBXBuildFile; fileRef = 581F23AC2A8CF92100788AB6 /* MockDefaultPathObserver.swift */; };
+		581F23AF2A8CF94D00788AB6 /* MockPinger.swift in Sources */ = {isa = PBXBuildFile; fileRef = 581F23AE2A8CF94D00788AB6 /* MockPinger.swift */; };
 		5820676426E771DB00655B05 /* TunnelManagerErrors.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5820676326E771DB00655B05 /* TunnelManagerErrors.swift */; };
 		5820EDA9288FE064006BF4E4 /* DeviceManagementInteractor.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5820EDA8288FE064006BF4E4 /* DeviceManagementInteractor.swift */; };
 		5820EDAB288FF0D2006BF4E4 /* DeviceRowView.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5820EDAA288FF0D2006BF4E4 /* DeviceRowView.swift */; };
@@ -373,6 +376,8 @@
 		58E45A5729F12C5100281ECF /* Result+Extensions.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58F1311427E0B2AB007AC5BC /* Result+Extensions.swift */; };
 		58E511E628DDDEAC00B0BCDE /* CodingErrors+CustomErrorDescription.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58E511E528DDDEAC00B0BCDE /* CodingErrors+CustomErrorDescription.swift */; };
 		58E511E828DDDF2400B0BCDE /* CodingErrors+CustomErrorDescription.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58E511E528DDDEAC00B0BCDE /* CodingErrors+CustomErrorDescription.swift */; };
+		58EC067A2A8D208D00BEB973 /* MockTunnelDeviceInfo.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58EC06792A8D208D00BEB973 /* MockTunnelDeviceInfo.swift */; };
+		58EC067C2A8D2A0B00BEB973 /* NetworkCounters.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58EC067B2A8D2A0B00BEB973 /* NetworkCounters.swift */; };
 		58EE2E3A272FF814003BFF93 /* SettingsDataSource.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58EE2E38272FF814003BFF93 /* SettingsDataSource.swift */; };
 		58EE2E3B272FF814003BFF93 /* SettingsDataSourceDelegate.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58EE2E39272FF814003BFF93 /* SettingsDataSourceDelegate.swift */; };
 		58EF580B25D69D7A00AEBA94 /* ProblemReportSubmissionOverlayView.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58EF580A25D69D7A00AEBA94 /* ProblemReportSubmissionOverlayView.swift */; };
@@ -952,6 +957,7 @@
 		5808273B284888BC006B77A4 /* App.xcconfig */ = {isa = PBXFileReference; lastKnownFileType = text.xcconfig; path = App.xcconfig; sourceTree = "<group>"; };
 		5808273C284888E5006B77A4 /* PacketTunnel.xcconfig */ = {isa = PBXFileReference; lastKnownFileType = text.xcconfig; path = PacketTunnel.xcconfig; sourceTree = "<group>"; };
 		580909D22876D09A0078138D /* RevokedDeviceViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = RevokedDeviceViewController.swift; sourceTree = "<group>"; };
+		58092E532A8B832E00C3CC72 /* TunnelMonitorTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = TunnelMonitorTests.swift; sourceTree = "<group>"; };
 		580CBFB72848D503007878F0 /* OperationConditionTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = OperationConditionTests.swift; sourceTree = "<group>"; };
 		580EE22324B3243100F9D8A1 /* AsyncBlockOperation.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AsyncBlockOperation.swift; sourceTree = "<group>"; };
 		580F8B8228197881002E0998 /* TunnelSettingsV2.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = TunnelSettingsV2.swift; sourceTree = "<group>"; };
@@ -974,6 +980,8 @@
 		5819C2162729595500D6EC38 /* SettingsAddDNSEntryCell.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SettingsAddDNSEntryCell.swift; sourceTree = "<group>"; };
 		581DA2722A1E227D0046ED47 /* RESTTypes.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = RESTTypes.swift; sourceTree = "<group>"; };
 		581DA2742A1E283E0046ED47 /* WgKeyRotation.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = WgKeyRotation.swift; sourceTree = "<group>"; };
+		581F23AC2A8CF92100788AB6 /* MockDefaultPathObserver.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = MockDefaultPathObserver.swift; sourceTree = "<group>"; };
+		581F23AE2A8CF94D00788AB6 /* MockPinger.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = MockPinger.swift; sourceTree = "<group>"; };
 		5820675A26E6576800655B05 /* RelayCache.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = RelayCache.swift; sourceTree = "<group>"; };
 		5820675D26E6839900655B05 /* PresentAlertOperation.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = PresentAlertOperation.swift; sourceTree = "<group>"; };
 		5820676326E771DB00655B05 /* TunnelManagerErrors.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = TunnelManagerErrors.swift; sourceTree = "<group>"; };
@@ -1224,6 +1232,8 @@
 		58E511E528DDDEAC00B0BCDE /* CodingErrors+CustomErrorDescription.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "CodingErrors+CustomErrorDescription.swift"; sourceTree = "<group>"; };
 		58E511EA28DDE18400B0BCDE /* Error+Chain.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "Error+Chain.swift"; sourceTree = "<group>"; };
 		58E973DD24850EB600096F90 /* AsyncOperation.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AsyncOperation.swift; sourceTree = "<group>"; };
+		58EC06792A8D208D00BEB973 /* MockTunnelDeviceInfo.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = MockTunnelDeviceInfo.swift; sourceTree = "<group>"; };
+		58EC067B2A8D2A0B00BEB973 /* NetworkCounters.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = NetworkCounters.swift; sourceTree = "<group>"; };
 		58ECD29123F178FD004298B6 /* Screenshots.xcconfig */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.xcconfig; path = Screenshots.xcconfig; sourceTree = "<group>"; };
 		58EE2E38272FF814003BFF93 /* SettingsDataSource.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = SettingsDataSource.swift; sourceTree = "<group>"; };
 		58EE2E39272FF814003BFF93 /* SettingsDataSourceDelegate.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = SettingsDataSourceDelegate.swift; sourceTree = "<group>"; };
@@ -2198,6 +2208,8 @@
 			isa = PBXGroup;
 			children = (
 				58C7A46F2A8649ED0060C66F /* PingerTests.swift */,
+				58092E532A8B832E00C3CC72 /* TunnelMonitorTests.swift */,
+				58EC067D2A8D2B0700BEB973 /* Mocks */,
 			);
 			path = PacketTunnelCoreTests;
 			sourceTree = "<group>";
@@ -2395,6 +2407,17 @@
 			path = TunnelMonitor;
 			sourceTree = "<group>";
 		};
+		58EC067D2A8D2B0700BEB973 /* Mocks */ = {
+			isa = PBXGroup;
+			children = (
+				581F23AC2A8CF92100788AB6 /* MockDefaultPathObserver.swift */,
+				581F23AE2A8CF94D00788AB6 /* MockPinger.swift */,
+				58EC06792A8D208D00BEB973 /* MockTunnelDeviceInfo.swift */,
+				58EC067B2A8D2A0B00BEB973 /* NetworkCounters.swift */,
+			);
+			path = Mocks;
+			sourceTree = "<group>";
+		};
 		58ECD29023F178FD004298B6 /* Configurations */ = {
 			isa = PBXGroup;
 			children = (
@@ -3436,6 +3459,11 @@
 			isa = PBXSourcesBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				58EC067A2A8D208D00BEB973 /* MockTunnelDeviceInfo.swift in Sources */,
+				58EC067C2A8D2A0B00BEB973 /* NetworkCounters.swift in Sources */,
+				581F23AD2A8CF92100788AB6 /* MockDefaultPathObserver.swift in Sources */,
+				58092E542A8B832E00C3CC72 /* TunnelMonitorTests.swift in Sources */,
+				581F23AF2A8CF94D00788AB6 /* MockPinger.swift in Sources */,
 				58C7A4702A8649ED0060C66F /* PingerTests.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
diff --git a/ios/PacketTunnelCore/Pinger/Pinger.swift b/ios/PacketTunnelCore/Pinger/Pinger.swift
index c312f822a4..e9a960a102 100644
--- a/ios/PacketTunnelCore/Pinger/Pinger.swift
+++ b/ios/PacketTunnelCore/Pinger/Pinger.swift
@@ -150,7 +150,7 @@ public final class Pinger: PingerProtocol {
             throw Error.sendPacket(errno)
         }
 
-        return PingerSendResult(sequenceNumber: sequenceNumber, bytesSent: UInt16(bytesSent))
+        return PingerSendResult(sequenceNumber: sequenceNumber, bytesSent: UInt(bytesSent))
     }
 
     private func nextSequenceNumber() -> UInt16 {
diff --git a/ios/PacketTunnelCore/Pinger/PingerProtocol.swift b/ios/PacketTunnelCore/Pinger/PingerProtocol.swift
index 6b7a4f9764..9df205ab6d 100644
--- a/ios/PacketTunnelCore/Pinger/PingerProtocol.swift
+++ b/ios/PacketTunnelCore/Pinger/PingerProtocol.swift
@@ -16,7 +16,7 @@ public enum PingerReply {
 
 public struct PingerSendResult {
     public var sequenceNumber: UInt16
-    public var bytesSent: UInt16
+    public var bytesSent: UInt
 }
 
 public protocol PingerProtocol {
diff --git a/ios/PacketTunnelCoreTests/Mocks/MockDefaultPathObserver.swift b/ios/PacketTunnelCoreTests/Mocks/MockDefaultPathObserver.swift
new file mode 100644
index 0000000000..2e6c4feb6e
--- /dev/null
+++ b/ios/PacketTunnelCoreTests/Mocks/MockDefaultPathObserver.swift
@@ -0,0 +1,48 @@
+//
+//  MockDefaultPathObserver.swift
+//  PacketTunnelCoreTests
+//
+//  Created by pronebird on 16/08/2023.
+//  Copyright © 2023 Mullvad VPN AB. All rights reserved.
+//
+
+import Foundation
+import NetworkExtension
+import PacketTunnelCore
+
+struct MockNetworkPath: NetworkPath {
+    var status: NetworkExtension.NWPathStatus = .satisfied
+}
+
+/// Mock implementation of a default path observer.
+class MockDefaultPathObserver: DefaultPathObserverProtocol {
+    var defaultPath: NetworkPath? {
+        return stateLock.withLock { innerPath }
+    }
+
+    private var innerPath: NetworkPath = MockNetworkPath()
+    private var stateLock = NSLock()
+
+    private var defaultPathHandler: ((NetworkPath) -> Void)?
+
+    func start(_ body: @escaping (NetworkPath) -> Void) {
+        stateLock.withLock {
+            defaultPathHandler = body
+        }
+    }
+
+    func stop() {
+        stateLock.withLock {
+            defaultPathHandler = nil
+        }
+    }
+
+    /// Simulate network path update.
+    func updatePath(_ newPath: NetworkPath) {
+        let pathHandler = stateLock.withLock {
+            innerPath = newPath
+            return defaultPathHandler
+        }
+        pathHandler?(newPath)
+    }
+}
diff --git a/ios/PacketTunnelCoreTests/Mocks/MockPinger.swift b/ios/PacketTunnelCoreTests/Mocks/MockPinger.swift
new file mode 100644
index 0000000000..e75918d0ad
--- /dev/null
+++ b/ios/PacketTunnelCoreTests/Mocks/MockPinger.swift
@@ -0,0 +1,126 @@
+//
+//  MockPinger.swift
+//  PacketTunnelCoreTests
+//
+//  Created by pronebird on 16/08/2023.
+//  Copyright © 2023 Mullvad VPN AB. All rights reserved.
+//
+
+import Foundation
+import Network
+@testable import PacketTunnelCore
+
+/// Ping client mock implementation that can be used to simulate network transmission errors and delays.
+class MockPinger: PingerProtocol {
+    typealias OutcomeDecider = (IPv4Address, UInt16) -> Outcome
+
+    private let decideOutcome: OutcomeDecider
+    private let networkStatsReporting: NetworkStatsReporting
+    private let stateLock = NSLock()
+    private var state = State()
+
+    var onReply: ((PingerReply) -> Void)? {
+        get {
+            stateLock.withLock { state.onReply }
+        }
+        set {
+            stateLock.withLock { state.onReply = newValue }
+        }
+    }
+
+    init(networkStatsReporting: NetworkStatsReporting, decideOutcome: @escaping OutcomeDecider) {
+        self.networkStatsReporting = networkStatsReporting
+        self.decideOutcome = decideOutcome
+    }
+
+    func openSocket(bindTo interfaceName: String?) throws {
+        stateLock.withLock {
+            state.isSocketOpen = true
+        }
+    }
+
+    func closeSocket() {
+        stateLock.withLock {
+            state.isSocketOpen = false
+        }
+    }
+
+    func send(to address: IPv4Address) throws -> PingerSendResult {
+        // Used for simulation. In reality can be any number.
+        // But for realism it is: IPv4 header (20 bytes) + ICMP header (8 bytes)
+        let icmpPacketSize: UInt = 28
+
+        let nextSequenceId = try stateLock.withLock {
+            guard state.isSocketOpen else { throw POSIXError(.ENOTCONN) }
+
+            return state.incrementSequenceId()
+        }
+
+        switch decideOutcome(address, nextSequenceId) {
+        case let .sendReply(reply, delay):
+            DispatchQueue.main.asyncAfter(deadline: .now() + delay) { [weak self] in
+                guard let self else { return }
+
+                networkStatsReporting.reportBytesReceived(UInt64(icmpPacketSize))
+
+                switch reply {
+                case .normal:
+                    onReply?(.success(address, nextSequenceId))
+                case .malformed:
+                    onReply?(.parseError(ParseError()))
+                }
+            }
+
+        case .ignore:
+            break
+
+        case .sendFailure:
+            throw POSIXError(.ECONNREFUSED)
+        }
+
+        networkStatsReporting.reportBytesSent(UInt64(icmpPacketSize))
+
+        return PingerSendResult(sequenceNumber: nextSequenceId, bytesSent: icmpPacketSize)
+    }
+
+    // MARK: - Types
+
+    /// Internal state
+    private struct State {
+        var sequenceId: UInt16 = 0
+        var isSocketOpen = false
+        var onReply: ((PingerReply) -> Void)?
+
+        mutating func incrementSequenceId() -> UInt16 {
+            sequenceId += 1
+            return sequenceId
+        }
+    }
+
+    /// Simulated ICMP reply.
+    enum Reply {
+        /// Simulate normal ping reply.
+        case normal
+
+        /// Simulate malformed ping reply.
+        case malformed
+    }
+
+    /// The outcome of ping request simulation.
+    enum Outcome {
+        /// Simulate ping reply transmission.
+        case sendReply(reply: Reply = .normal, afterDelay: TimeInterval = 0.1)
+
+        /// Simulate packet that was lost or left unanswered.
+        case ignore
+
+        /// Simulate failure to send ICMP packet (i.e `sendto()` error).
+        case sendFailure
+    }
+
+    struct ParseError: LocalizedError {
+        var errorDescription: String? {
+            return "ICMP response parse error"
+        }
+    }
+}
diff --git a/ios/PacketTunnelCoreTests/Mocks/MockTunnelDeviceInfo.swift b/ios/PacketTunnelCoreTests/Mocks/MockTunnelDeviceInfo.swift
new file mode 100644
index 0000000000..bb61dfb443
--- /dev/null
+++ b/ios/PacketTunnelCoreTests/Mocks/MockTunnelDeviceInfo.swift
@@ -0,0 +1,26 @@
+//
+//  MockTunnelDeviceInfo.swift
+//  PacketTunnelCoreTests
+//
+//  Created by pronebird on 16/08/2023.
+//  Copyright © 2023 Mullvad VPN AB. All rights reserved.
+//
+
+import Foundation
+import PacketTunnelCore
+
+/// Mock implementation of a tunnel device.
+struct MockTunnelDeviceInfo: TunnelDeviceInfoProtocol {
+    let networkStatsProviding: NetworkStatsProviding
+
+    var interfaceName: String? {
+        return "utun0"
+    }
+
+    func getStats() throws -> WgStats {
+        return WgStats(
+            bytesReceived: networkStatsProviding.bytesReceived,
+            bytesSent: networkStatsProviding.bytesSent
+        )
+    }
+}
diff --git a/ios/PacketTunnelCoreTests/Mocks/NetworkCounters.swift b/ios/PacketTunnelCoreTests/Mocks/NetworkCounters.swift
new file mode 100644
index 0000000000..d20a1ef20f
--- /dev/null
+++ b/ios/PacketTunnelCoreTests/Mocks/NetworkCounters.swift
@@ -0,0 +1,54 @@
+//
+//  NetworkCounters.swift
+//  PacketTunnelCoreTests
+//
+//  Created by pronebird on 16/08/2023.
+//  Copyright © 2023 Mullvad VPN AB. All rights reserved.
+//
+
+import Foundation
+
+/// Protocol describing a type capable of receiving and updating network counters.
+protocol NetworkStatsReporting {
+    /// Increment number of bytes sent.
+    func reportBytesSent(_ byteCount: UInt64)
+
+    /// Increment number of bytes received.
+    func reportBytesReceived(_ byteCount: UInt64)
+}
+
+/// Protocol describing a type providing network statistics.
+protocol NetworkStatsProviding {
+    /// Returns number of bytes sent.
+    var bytesSent: UInt64 { get }
+
+    /// Returns number of bytes received.
+    var bytesReceived: UInt64 { get }
+}
+
+/// Class that holds network statistics (bytes sent and received) for a simulated network adapter.
+final class NetworkCounters: NetworkStatsProviding, NetworkStatsReporting {
+    private let stateLock = NSLock()
+    private var _bytesSent: UInt64 = 0
+    private var _bytesReceived: UInt64 = 0
+
+    var bytesSent: UInt64 {
+        stateLock.withLock { _bytesSent }
+    }
+
+    var bytesReceived: UInt64 {
+        stateLock.withLock { _bytesReceived }
+    }
+
+    func reportBytesSent(_ byteCount: UInt64) {
+        stateLock.withLock {
+            _bytesSent += byteCount
+        }
+    }
+
+    func reportBytesReceived(_ byteCount: UInt64) {
+        stateLock.withLock {
+            _bytesReceived += byteCount
+        }
+    }
+}
diff --git a/ios/PacketTunnelCoreTests/TunnelMonitorTests.swift b/ios/PacketTunnelCoreTests/TunnelMonitorTests.swift
new file mode 100644
index 0000000000..462c2f1476
--- /dev/null
+++ b/ios/PacketTunnelCoreTests/TunnelMonitorTests.swift
@@ -0,0 +1,119 @@
+//
+//  TunnelMonitorTests.swift
+//  PacketTunnelCoreTests
+//
+//  Created by pronebird on 15/08/2023.
+//  Copyright © 2023 Mullvad VPN AB. All rights reserved.
+//
+
+import Network
+@testable import PacketTunnelCore
+import XCTest
+
+final class TunnelMonitorTests: XCTestCase {
+    let networkCounters = NetworkCounters()
+
+    func testShouldDetermineConnectionEstablished() throws {
+        let connectedExpectation = expectation(description: "Should report connected.")
+        let connectionLostExpectation = expectation(description: "Should not report connection loss")
+        connectionLostExpectation.isInverted = true
+
+        let pinger = MockPinger(networkStatsReporting: networkCounters) { destination, sequence in
+            return .sendReply()
+        }
+
+        let tunnelMonitor = TunnelMonitor(
+            eventQueue: .main,
+            pinger: pinger,
+            tunnelDeviceInfo: MockTunnelDeviceInfo(networkStatsProviding: networkCounters),
+            defaultPathObserver: MockDefaultPathObserver()
+        )
+
+        tunnelMonitor.onEvent = { event in
+            switch event {
+            case .connectionEstablished:
+                connectedExpectation.fulfill()
+
+            case .connectionLost:
+                connectionLostExpectation.fulfill()
+
+            case .networkReachabilityChanged:
+                break
+            }
+        }
+
+        tunnelMonitor.start(probeAddress: .loopback)
+
+        waitForExpectations(timeout: 1)
+    }
+
+    func testInitialConnectionTimings() {
+        // Setup pinger so that it never receives any replies.
+        let pinger = MockPinger(networkStatsReporting: networkCounters) { destination, sequence in
+            return .ignore
+        }
+
+        let tunnelMonitor = TunnelMonitor(
+            eventQueue: .main,
+            pinger: pinger,
+            tunnelDeviceInfo: MockTunnelDeviceInfo(networkStatsProviding: networkCounters),
+            defaultPathObserver: MockDefaultPathObserver()
+        )
+
+        /*
+         Tunnel monitor uses shorter timeout intervals during the initial connection sequence and picks next relay more
+         aggressively in order to reduce connection time.
+
+         First connection attempt starts at 4 second timeout, then doubles with each subsequent attempt, while being
+         capped at 15s max.
+         */
+        var expectedTimings = [4, 8, 15, 15]
+
+        // Calculate the amount of time necessary to perform the test adding some leeway.
+        let timeout = expectedTimings.reduce(1, +)
+
+        let expectation = self.expectation(description: "Should respect all timings.")
+        expectation.expectedFulfillmentCount = expectedTimings.count
+
+        // This date will be used to measure the amount of time elapsed between `.connectionLost` events.
+        var startDate = Date()
+
+        tunnelMonitor.onEvent = { [weak tunnelMonitor] event in
+            guard case .connectionLost = event else { return }
+
+            switch event {
+            case .connectionLost:
+                let expectedDuration = expectedTimings.removeFirst()
+
+                // Compute amount of time elapsed between `.connectionLost` events rounding it down towards zero.
+                let timeElapsed = Int(Date().timeIntervalSince(startDate).rounded(.down))
+
+                XCTAssertEqual(
+                    timeElapsed,
+                    expectedDuration,
+                    "Expected to report connection loss after \(expectedDuration)s, instead reported it after \(timeElapsed)s."
+                )
+
+                expectation.fulfill()
+
+                if !expectedTimings.isEmpty {
+                    startDate = Date()
+
+                    // Continue monitoring by calling start() again.
+                    tunnelMonitor?.start(probeAddress: .loopback)
+                }
+
+            case .connectionEstablished:
+                XCTFail()
+
+            case .networkReachabilityChanged:
+                break
+            }
+        }
+
+        // Start monitoring.
+        tunnelMonitor.start(probeAddress: .loopback)
+
+        waitForExpectations(timeout: TimeInterval(timeout))
+    }
+}