How to send a mock object as JSON in mockmvc

Question

I want to send a mock object in the controller via MockMvc with content type JSON. But when I am trying to serialize the mock the error is:

java.lang.UnsupportedOperationException: Expecting parameterized type, got interface org.mockito.internal.MockitoInvocationHandler.
 Are you missing the use of TypeToken idiom?

My code is as following:

@Test
public void testSomething(){

    String xyz = "";
    Integer i = 10;
    SomeClass inst = mock(SomeClass.class, withSettings().serializable());
    when(inst.getProperty1()).then(xyz);
    when(inst.getProperty2()).then(i);

    Gson gson = new Gson();
    String json = gson.toJson(inst); // this is creating error

    this.mockmvc.perform(put("/someUrl/").contentType(MediaType.JSON).content(json)).andExpect(status().isOk());
}

Can someone tell me what I'm missing?

Answer 1

I propose that you create a stub of your SomeClass that returns known values for the getProperty1() and getProperty2() method. Depending on how SomeClass is implemented, you could either create a new instance of it directly, subclass and override some methods, create an anonymous inner class if it is an interface, etc.

@Test
public void testSomething(){

    String xyz = "";
    Integer i = 10;

    // alt 1:
    SomeClass stub = new SomeClass(xyz, i);

    // alt 2: 
    SomeClass stub = new StubSomeClass(xyz, i); // StubSomeClass extends SomeClass

    // alt 3: 
    SomeClass stub = new SomeClass() {
         @Override
         String getProperty1() {
             return xyz;
         }
         @Override
         Integer getProperty2() {
             return i;
         }
    }

    Gson gson = new Gson();
    String json = gson.toJson(stub);

    this.mockmvc.perform(put("/someUrl/")
        .contentType(MediaType.APPLICATION_JSON).content(json))
        .andExpect(status().isOk());
}

Answer 2

Even if it was possible, submitting a mock object to a JSON converter would suppose a unit test dedicated to that operation : the mock object may have many attributes and methods far beyond the real class and the serialization could lead to a really strange result.

IMHO, as it is a unit test, you should write by hand the json serialized String. And you can do other tests if you need to control how Gson does the serialization