Testing method without parameters

This is one my first times posting on here so I'll do my best to be concise and clear.

My method below takes in 0 arguments and reads through a certain file looking for a tag to echo to the console:

protected static serverVersion() {
    String output = "";
    try {
        File lsbRelease = new File("/path/randomFile.txt");
        BufferedReader br = new BufferedReader(new InputStreamReader(lsbRelease));
        boolean isMatch = false;
        String line = "";

        // run through file and find the tag
        (...)

The three different possibilities of the method are:

1. Read the correct file, find the tag and echo the tag
2. Read the correct file, does not find the tag and outputs a message to the user
3. Not able to read the file, throw exception

Is there a way for me to write tests that simulate these three different situations? I thought about using the Rule for TemporaryFolder/Files, but I don't know how I would make the test use the temporary file I make.

I know I could pass in a string as a parameter for the file path and then use a TemporaryFile to test, but I want to avoid changing the original method. Also, I want to avoid using another framework (i.e. Mockito).