Gradle ExecAction mock for Spock tests

MockExecAction.groovy

class MockExecAction extends DefaultExecAction {
    int exitValue = 0
    String output = ''

    MockExecAction() {
        super(null, null, null)
    }

    @Override
    ExecResult execute() {
        standardOutput.write(output.getBytes('UTF-8'))

        ExecResult result = new ExecResult() {
            @Override
            int getExitValue() {
                MockExecAction.this.exitValue
            }

            @Override
            ExecResult assertNormalExitValue() throws ExecException {
                if (exitValue != 0) {
                    throw new ExecException("Command exited with ${exitValue}: ${getCommandLine().join(' ')}")
                }
                this
            }

            @Override
            ExecResult rethrowFailure() throws ExecException {
                assertNormalExitValue()
            }
        }
        result.assertNormalExitValue()
        result
    }
}

MockExecActionFactory.groovy

class MockExecActionFactory implements ExecActionFactory {
    MockExecAction mockExecAction = new MockExecAction()

    @Override
    ExecAction newExecAction() {
        mockExecAction
    }

    @Override
    JavaExecAction newJavaExecAction() {
        return null // TODO:
    }
}