How do you mock an object instantiated inside another object in Groovy?

Here's my example code

class CommandLine {

    def ls() {
        def cmd = "ls".execute开发者_高级运维()
        if(cmd.waitFor() != 0) {
            throw new Execution()
        }
        return cmd.text
    }
}

The cmd variable holds an object of type java.lang.Process. How would I mock out the waitFor() method in order to test the thrown exception? If I can't, is there some way this could be rewritten to facilitate automated testing?

In general, how do you mock an object instantiated inside another class, or how do you structure your code to allow for testing?

I'm not familiar with Groovy, but if there's a chance of mocking the method String#execute() to return a mocked Process with a method waitFor() which returns not zero result it would be the way to do it

Something like:

Process mockedProcess = MockingFramework.mock(Process.class); // MockingFramework can be Mockito
MockingFramework.when(String.execute()).thenReturn(mockedProcess);
MockingFramework.when(mockedProcess.waitFor).thenReturn(1);

new CommandLine().ls(); // Boom! => Execution exception

The answer is to use Groovy mocks instead of the built in Grails mocks.

import groovy.mock.interceptor.MockFor

class TestClass {

    def test() {
        def mock = new MockFor(classToBeMocked)

        mock.demand.methodToBeMocked(1..1) { -> /* code */ }

        mock.use {
            /*
            All calls to objects of type classToBeMocked will be 
            intercepted within this block of code.
            */
        }
    }
}