These are the unit tests for iOS engine. They can be executed locally and are also run in LUCI builds.
testing/run_tests.py [--type=objc]
After the ios_test_flutter target is built you can also run the tests inside of Xcode with testing/ios/IosUnitTests/IosUnitTests.xcodeproj. If you modify the test or under-test files, you'll have to run run_tests.py again.
When you add a new unit test file, also add a reference to that file in shell/platform/darwin/ios/BUILD.gn, under the sources list of the ios_test_flutter target. Once it's there, it will execute with the other tests.