How to use xcodebuild with -only-testing and -skip-testing flag?

Like what Marcio said, it's a path like string.

For example, say you have a scheme named MyScheme, a test target MyUITests, and testing class LoginTest, then testing method testUserLogin, to run only the method, you can run

xcodebuild -workspace Envoy.xcworkspace \
    -scheme MyScheme \
    -sdk iphonesimulator \
    -destination 'platform=iOS Simulator,name=iPad Air 2,OS=10.1'
    '-only-testing:MyUITests/LoginTest/testUserLogin' test

Likewise, if you want to run all tests under LoginTest, here you run

xcodebuild -workspace Envoy.xcworkspace \
    -scheme MyScheme \
    -sdk iphonesimulator \
    -destination 'platform=iOS Simulator,name=iPad Air 2,OS=10.1'
    '-only-testing:MyUITests/LoginTest' test

In case you need to include several tests:

xcodebuild -project Some.xcodeproj \
-scheme AllTests -only-testing:PersistenceTests -only-testing:FoundationTests test

Documentation:

An xcodebuild command can combine multiple constraint options, but -only-testing: has precedence over -skip-testing:.

You can check the video https://developer.apple.com/videos/play/wwdc2016/409/

I used it like this:

-only-testing:UITests/TC_TextArea/test1

for my tests tree. Works fine

Full command looks as follows:

command = 'xcodebuild test 
-workspace ' + pathToProjectWorkspaceFolder + '/project.xcworkspace 
-scheme yourApp.app 
-destination "platform=iOS,name=' + deviceName + '" 
-only-testing:UITests/TC_TextArea/test1'