Mockito java - 模拟第三方实用方法和私有方法调用

Question

I have a legacy code which has some methods like below:

public void display(String fileName, Path path){
    //do some stuff
    Files.exists(path);
    if(null==privateMethod(fileName))
       //something
}

private Object privateMethod(String fileName){
   // do something
   return object;
}

I am writing tests(using mockito) for display method. How do I get around calls like Files.exists(path) and internal private method calls because I think normal stubbing cannot used with private method(visibility issue). As Files.exists() is utility method so cannot be mocked. Do I need to actually create some test files in testing method and probably delete them? Or is there a better clean way. Also I have searched regarding private method testing - everyone suggests powermock which Iam not allowed to use. Anyway I don't need to test private method but bypass/stub their call returns.

Answer 1

In this case makes sense to have some files for testing. You can generate them or create them in advance in the folder src/test/resources .

For example a test might look like this:

@Test
public void myTest(){
    // MyFile.txt is in src/test/resources
    Path path = Paths.get("src","test","resources"); 
    service.display("MyFile.txt", path);
    // Asserts..
}

Regarding mocking private methods, in general is not recommended because your test will depend on implementation details of your class, so I strongly discourage it. Furthermore, if you are not allowed to use Powermock it might not be possible at all.

But there are alternatives, for example if the private method uses some external services or libraries, than you can mock them instead of the whole method. The idea is to mock the external entities that the class depends on rather than parts of the class itself.