Question

I was looking at android source code and i found this code.

/**
 * Interface used in {@link #createUniqueFile} instead of {@link File#createNewFile()} to make
 * it testable.
 */
/* package */ interface NewFileCreator {
    public static final NewFileCreator DEFAULT = new NewFileCreator() {
                @Override public boolean createNewFile(File f) throws IOException {
                    return f.createNewFile();
                }
    };
    public boolean createNewFile(File f) throws IOException ;
}

How is it more testable? And can anybody redirect me to the place where i can see more examples?

Answer 1

The reason is so that in your tests you can substitute the NewFileCreator with a different implementation wherever it’s being used – one that just saves the data in memory for example.

This means you can test the logic of whatever’s using this without worrying about making sure a real filesystem exists and that it’s in a suitable state.