There's a problem with this code:

Rather than calling exit(-1) directly, it should instead call the wrapper exitApp(-1):

The subclass TestContext overwrites exitApp to throw an exception:

So calling exit(-1) directly would terminate the test process directly, rather than throwing an exception.

Solution

short term

Replace exit with exitApp

Long term

This is another drawback of the current design using inheritance (see discussion #173133). It's too easy to introduce bugs like this if we keep this design.

Instead, we should inject an abstraction layer, say "Host":

// excuse my poor dart syntax, but you get the idea
abstract class Host {
  Never exit(int code);
  // other members like stdout/stderr
}

class RealHost: Host {
  Never exit(int code) {
    dart.io.exit(code);
  }
}

class FakeHost: Host {
  Never exit(int code) {
    throw Exception...
  }
}

Then xcode_backend.dart should just depend on the Host abstraction layer, without importing dart.io package.