Reproduction steps:
1. Open the attached project;
2. Click Window->Test Runner;
3. In Test Runner Window, select PlayMode tab;
4. Click "Run all in player (iOS)";
5. Observe the console.

Expected result: Tests are successfully performed, or a popup/warning appears, informing what needs to be set up for the iOS tests to work.
Actual results: an error is thrown to console:
Exception: Device ID not specified. Set IOS_DEVICE_ID environment variable for iOS tests and TVOS_DEVICE_ID for tvOS tests
UnityEditor.iOS.Extensions.Common.AppleCommandLineBuildAndRun.GetDeviceIdForTests (BuildTarget target) (at /Users/builduser/buildslave/unity/build/PlatformDependent/iPhonePlayer/Extensions/Common/AppleCommandLineBuildAndRun.cs:205)

Reproducible on: 2018.1.0a1, 2018.1.2f1, 2018.2.0b6, 2018.3.0a1.
Not reproduced on: 2017.4.4f1 and lower.

Note: on 2018.2 and 2018.3 error is a bit different:
AppleCommandLineBuildAndRunException: Xcodebuild failed building project
UnityEditor.iOS.Extensions.Common.AppleCommandLineBuildAndRun.LaunchXcodebuildBuild (System.String projectPath, BuildTarget target, Boolean configurationRelease) (at /Users/builduser/buildslave/unity/build/PlatformDependent/iPhonePlayer/Extensions/Common/AppleCommandLineBuildAndRun.cs:132)
UnityEditor.iOS.Extensions.Common.AppleCommandLineBuildAndRun.BuildAndRunWithiOSDeploy (BuildTarget target, System.String projectPath) (at /Users/builduser/buildslave/unity/build/PlatformDependent/iPhonePlayer/Extensions/Common/AppleCommandLineBuildAndRun.cs:34)
UnityEditor.iOS.PostProcessiPhonePlayer.Launch (BuildLaunchPlayerArgs args) (at /Users/builduser/buildslave/unity/build/PlatformDependent/iPhonePlayer/Extensions/Common/BuildPostProcessor.cs:2248)
UnityEditor.iOS.iOSBuildPostprocessor.LaunchPlayer (BuildLaunchPlayerArgs args) (at /Users/builduser/buildslave/unity/build/PlatformDependent/iPhonePlayer/Extensions/Common/ExtensionModule.cs:32)
UnityEditor.PostprocessBuildPlayer.Launch (BuildTargetGroup targetGroup, BuildTarget buildTarget, System.String path, System.String productName, BuildOptions options, UnityEditor.Build.Reporting.BuildReport buildReport) (at /Users/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/PostprocessBuildPlayer.cs:174)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)

Fixed in: 2018.3.0a6.