Testing a method by overriding a private class variable as an initial step before refactoring

Question

What is the best way of writing a unit test for a method, such as my setProperties (see below), that uses a private configuration variable (config). I tried but failed to override it using reflection and Makito, but without success. I realize that changing the design to make the code easier to test is best, but I want to created some unit tests before I refactor the code.

public class MainClass {
    private final java.lang.String config = "app.properties";

    public TestClass() {
        try {
            setProperties();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public void setProperties() throws Exception {
        try {
            InputStream input = new BufferedInputStream(new FileInputStream(config));
            ..
            ..
        } catch (Exception exception) {
            throw exception;
        }
    }
}

Post full code of `setProperties` method or the issue with mocking only config file? — Sergey Prokofiev, May 04 '18 at 05:30
Issue is mocking or overriding the private variable. I want a way to change the value for that private variable during the unit testing. — BoomRamada, May 04 '18 at 05:34
_"I couldn't do it with the reflection"_ - What did you actually try? Did you see https://stackoverflow.com/q/3301635/2587435? — Paul Samsotha, May 04 '18 at 06:49

score 1 · Answer 1 · answered May 04 '18 at 06:45

1

Do refactor a tiny bit by extracting a method with a parameter that takes an input stream. Call this new method (probably package-protected) from the old one. Write tests against the new method. Then do more refactorings.

answered May 04 '18 at 06:45

Arne Deutsch

14,629
5
53
72

score 0 · Answer 2 · answered May 04 '18 at 05:41

This is an indication of a broken design; don't hard-code things like this. Better yet, determine what the appropriate responsibility for this class is, and, in decreasing order of preference:

pass in an object with the configuration properties, strongly typed
pass in a Map with the configuration properties
pass in an InputStream for the properties file

As File objects are never available from a jar, you shouldn't ever make interfaces like this more specific than InputStream or Reader, so that you can always pass in streams from your jar classpath.

I'm aware of the issue, I'm after solution for unit test before refactor. Unfortunately this code is not own by me and unchangeable. — BoomRamada, May 04 '18 at 05:50

score 0 · Answer 3 · answered May 04 '18 at 05:47

So you can use Properties class in Java for this. Please have a look at this code.

public class PropertyUtil {

        private static Properties prop;

        private static Logger logger = Logger.getLogger(PropertyUtil.class);

        private PropertyUtil() {

        }

        public void setProperty() {
            String filePath = System.getenv("JAVA_HOME") + "/lib" + "/my_file.properties";
            prop = new Properties();

            try (InputStream input = new FileInputStream(filePath)) {
                prop.load(input);
            } catch (IOException ex) {
                logger.error("Error while reading property file " + ex);
            }
        }

        public static String getProperty(String key) {
            if (prop.containsKey(key)) {
                return prop.getProperty(key);
            } else {
                return null;
            }
        }

        public static <T> T getProperty(String key, Class<T> claz) {

            if (claz.getName().equals(Integer.class.getName())) {
                return claz.cast(Integer.parseInt(prop.getProperty(key)));
            }
            if (claz.getName().equals(Long.class.getName())) {
                return claz.cast(Long.parseLong(prop.getProperty(key)));
            }
            if (claz.getName().equals(Boolean.class.getName())) {
                return claz.cast(Boolean.parseBoolean(prop.getProperty(key)));
            }
            if (claz.getName().equals(Double.class.getName())) {
                return claz.cast(Double.parseDouble(prop.getProperty(key)));
            }
            if (claz.getName().equals(String.class.getName())) {
                return claz.cast(prop.getProperty(key));
            }

            return null;
        }

Testing a method by overriding a private class variable as an initial step before refactoring

3 Answers3