Using Spring's MockMvc framework, how do I test the value of an attribute of an attribute of my model?

You can nest hasItem and hasProperty matchers if your object has a getter getMyProperty.

.andExpect(model().attribute("MyObjectForm",
   hasProperty("myObjects",
       hasItem(hasProperty("myProperty”, Matchers.equalTo(true))))))

If you know how much objects are in the list than you can check the first item with

.andExpect(model().attribute("MyObjectForm",
   hasProperty("myObjects", contains(
         hasProperty("myProperty”, Matchers.equalTo(true)),
         any(MyObject.class),
         ...
         any(MyObject.class)))));