How can I unit test this inputStream has been closed?

Question

I have a Runnable along the lines of:

    public void run() {
        InputStream inputStream = null;
        try {
            inputStream = new FileInputStream(file);
            //more stuff here
        } 
        catch (Exception e) {
            //simplified for reading
        }
        finally {
            if(inputStream != null) {
                try {
                    inputStream.close();
                } catch (IOException e) {}
            }
        }
    }

How do I test inputStream.close() was invoked? I am currently using Mockito and JUnit. I know injecting the inputStream in is an idea, but I don't want the resources to be used until run?() is called, hence it being a local variable. So how can I redesign my code in a way that allows me to test whether close was called?

Answer 1

If I understood the task correctly it could be like this

static boolean isClosed;

public void run() {
    InputStream inputStream = null;
    try {
        inputStream = new FileInputStream(file) {
            @Override
            public void close() throws IOException {
                isClosed = true;
                super.close();
            }
        };
        // more stuff here