XCTests canceling prematurely

Question

I am running a few unit tests inside Xcode with XCTests. When I run them, all the tests either pass and fail and show the little green check or red cross. The main issue seems to be that my tests are prematurely canceling and they are not being run properly.

Here's some more information:

1. When the tests are run, there is no console output whatsoever which was not happening before. By that I mean I did have the expected console output before, now I don't.
2. When the tests are run, it does not require me to unlock my iPhone so that the app can run. Moreover, even if my iPhone is unlocked, it doesn't run the application which it would do before.

3. When running my tests, it finishes compiling and then very quickly says "Canceling..." in the information bar in Xcode (the top and centered bar that shows warnings and "Building " when you build your project).

4. I am using the .xcworkspace file (becasue I am using Pods)

5. I have one build scheme which is the project.
6. I had these same issues plus the issues of the green checks and red crosses not showing up on my tests after they ran and the sometimes my tests not showing up at all in the testing tab. I fixed these issues by deleting the Podfile.lock file, Pods directory, and the .xcworkspace directory and then running Pod install. After doing this, I had the same issues, except those two issues.
7. I tried running new tests on a different branch, same issues.

8. Before running into any of these issues, I was just writing tests and trying different methods of writing tests. I've reverted all those changes and I still get these errors.

9. I have also found the same issues when running the tests no the simulator.

10. When I compile and run the app from Xcode, it runs fine.

Any advice on how to solve this would be great! Please ask for more details if needed.

Here's a video of me running my tests. I set up a new project and new unit test target to show what's going on. Note: There's an empty test in there and a test that should always pass:

As you can see, the issue is the tests are not running properly. The green and red crosses are not showing up anymore, the test that's supposed to always pass is failing, there is no console output, and in the top information bar it's saying "canceling..." almost immediately. Any advice on why this canceling is happening would be great!

Here are some screenshots of how the code is set up:

Here's the code as well (it's just the basic code after creating a new unit test, except I added in one assert that should always pass):

import XCTest
@testable import example

class exampleTests: XCTestCase {

    override func setUp() {
        // Put setup code here. This method is called before the invocation of each test method in the class.
    }

    override func tearDown() {
        // Put teardown code here. This method is called after the invocation of each test method in the class.
    }

    func testExample() {
        // This is an example of a functional test case.
        // Use XCTAssert and related functions to verify your tests produce the correct results.
        XCTAssertTrue(true)
    }

    func testPerformanceExample() {
        // This is an example of a performance test case.
        self.measure {
            // Put the code you want to measure the time of here.
        }
    }
}

Edit:

So, as per @CPR's suggestion, I tried it again on the simulator and the errors were basically all gone. I tried it again on the physical device, but the errors persisted. Note: I had tried it before on the simulator and got the same errors. I didn't change anything since then so I am unsure of why it worked now. Here's the console output from running the tests on the sim (not sure if that will help, but I'll add it anyway):

Test Suite 'All tests' started at 2018-12-06 03:59:53.045
Test Suite 'exampleTests.xctest' started at 2018-12-06 03:59:53.046
Test Suite 'exampleTests' started at 2018-12-06 03:59:53.046
Test Case '-[exampleTests.exampleTests testExample]' started.
Test Case '-[exampleTests.exampleTests testExample]' passed (0.001 seconds).
Test Case '-[exampleTests.exampleTests testPerformanceExample]' started.
/Users/akashkundu/Documents/example/exampleTests/exampleTests.swift:30: Test Case '-[exampleTests.exampleTests testPerformanceExample]' measured [Time, seconds] average: 0.000, relative standard deviation: 115.251%, values: [0.000004, 0.000001, 0.000001, 0.000001, 0.000001, 0.000001, 0.000001, 0.000001, 0.000001, 0.000001], performanceMetricID:com.apple.XCTPerformanceMetric_WallClockTime, baselineName: "", baselineAverage: , maxPercentRegression: 10.000%, maxPercentRelativeStandardDeviation: 10.000%, maxRegression: 0.100, maxStandardDeviation: 0.100
Test Case '-[exampleTests.exampleTests testPerformanceExample]' passed (0.348 seconds).
Test Suite 'exampleTests' passed at 2018-12-06 03:59:53.396.
     Executed 2 tests, with 0 failures (0 unexpected) in 0.348 (0.350) seconds
Test Suite 'exampleTests.xctest' passed at 2018-12-06 03:59:53.396.
     Executed 2 tests, with 0 failures (0 unexpected) in 0.348 (0.350) seconds
Test Suite 'All tests' passed at 2018-12-06 03:59:53.397.
     Executed 2 tests, with 0 failures (0 unexpected) in 0.348 (0.351) seconds 

Can anyone shed some light on why running the tests on the physical device causes these errors?

Edit:

Here's the error/log message from the "Messages" tab in Xcode found by @CPR:

Here's the error/log code in text:

example.app encountered an error (Failed to establish communication with the test runner. (Underlying error: Unable to connect to test manager on 8b441d96d063b3b6abf55b06115441d160e85e67. (Underlying error: kAMDMuxConnectError: Could not connect to the device.)))

-----------------------------------------------------------------------

Solution:

Thanks to @CPR, the solution is to simply restart the device. Another lesson learned is to use the "Messages" tab to see logs and errors which is the right most tab next to the "Breakpoint" tab.

His full answer here.

Answer 1

Problem resolved in comments. For future readers, here are some good things to check if you encounter similar issues:

1. Check Xcode messages tab to look for build errors.
2. Restart device/simulator as appropriate. This fixed the problem in this case.
3. Uninstall/reinstall app on device/simulator.
4. Are certs/provisioning profiles valid? Try generating new ones and re-running.
5. Does it work on the simulator? If yes, this is likely an issue with the device itself.
6. Are breakpoints hit when you run the code? If yes, then this is a test failure. If no, the problem is happening before the tests are even run (as was the case here).