How to test that an instance method is called with certain arguments?

Question

I'm building a simple RESTful app (using Spark Java, although this question is more general).

The Handler below is called when the /users index route is requested. It just queries for all users and renders an HTML template (using Velocity, but again this question is more general).

package com.example.api;

import java.util.*;

import spark.Request;
import spark.ModelAndView;
import spark.template.velocity.VelocityTemplateEngine;

public class UsersIndexHandler {

  private Map<String, Object> locals;

  private UserDao userDao;

  public UsersIndexHandler(UserDao userDao) {
    this.locals = new HashMap<>();
    this.userDao = userDao;
  }

  public String execute(Request req, boolean formatAsHtml) {
    // Set locals so they are available in the view
    locals.put("users", userDao.all());

    // Render the view
    String body = new VelocityTemplateEngine().render(new ModelAndView(locals, "views/users/index.vm"))

    return body;
  }
}

I'm trying to write a basic Junit test for this scenario. I could test the contents of the String that's returned, but I have two issues with that -

1. The HTML for the page could be quite long, so it doesn't feel practical to do a direct comparison of the actual result with an expected test string

2. The content of view should be tested in a view test.

What's the "right" (generally accepted) way to test this? Is there a way to set expectations on VelocityTemplateEngine() so we know that render() is called correctly AND with correct arguments?

Or should I focus on just testing the locals Map object, even though I'd have to expose that to access it during tests?

Thanks!

Answer 1

I am in line with the views that Tom has mentioned in the comment but if still,

you want to follow this pattern, Powermockito (and plain Powermock also) have a way to do this. I will Just post an example here

Employee mockEmployeeObject = mock(Employee.class);

PowerMockito.whenNew(Employee.class)
            .withAnyArguments().thenReturn(mockEmployeeObject);

verify(mockEmployeeObject, times(1)).someMethod();

Powermockito.whenNew(..) lets us return our mocked object when any new object of that class is created, since you want to verify the method parameters, it works well for you. You can add the verify that you need I just posted an example.

Hope this helps!

Good luck!