Generic type erasure tests

GenericTypeTest.java

package com.goodercode;

import static org.hamcrest.CoreMatchers.equalTo;
import static org.hamcrest.CoreMatchers.not;
import static org.junit.Assert.assertThat;

import java.lang.reflect.ParameterizedType;
import java.lang.reflect.TypeVariable;

import org.junit.Before;
import org.junit.Test;

public class GenericTypeTest {

    private MyGenericClass instance;
    
    @Before
    public void setup() {
	instance = new MyGenericClass();
    }
    
    @Test
    public void can_get_generic_superclass_type() throws Exception {
	final ParameterizedType pt = (ParameterizedType)MyGenericClass.class.getGenericSuperclass();
	assertThat( (Class<Float>)pt.getActualTypeArguments()[0], equalTo(Float.class));
    }
    
    @Test
    public void can_get_generic_interface_type() throws Exception {
	final ParameterizedType pt = (ParameterizedType)MyGenericClass.class.getGenericInterfaces()[0];
	assertThat( (Class<Long>)pt.getActualTypeArguments()[0], equalTo(Long.class));
    }
    
    @Test 
    public void can_get_generic_method_return_type() throws Exception {
	final ParameterizedType pt = (ParameterizedType)MyGenericClass.class.getDeclaredMethod("genericMethodReturn").getGenericReturnType();
	assertThat( (Class<String>)pt.getActualTypeArguments()[0], equalTo(String.class));
    }
    
    @Test
    public void can_get_generic_method_parameter_type() throws Exception {
	final ParameterizedType pt = (ParameterizedType)MyGenericClass.class.getDeclaredMethod("genericMethodParameter", GenericInterface.class).getGenericParameterTypes()[0];
	assertThat( (Class<Double>)pt.getActualTypeArguments()[0], equalTo(Double.class));
    }
    
    @Test
    public void can_get_generic_local_interface_type() throws Exception {
	
	final GenericInterface<Float> local = new GenericInterface<Float>() {};
	final ParameterizedType pt = (ParameterizedType)local.getClass().getGenericInterfaces()[0];
	assertThat( (Class<Float>)pt.getActualTypeArguments()[0], equalTo(Float.class));
	
    }
    
    @Test
    public void cannot_get_generic_local_class_type() throws Exception {
	
	final GenericSuperclass local = new GenericSuperclass<Double>();
	final TypeVariable tv = local.getClass().getTypeParameters()[0];
	assertThat( (Class<String>)tv.getBounds()[0], not(equalTo(String.class)));
	
    } 
    
    public interface GenericInterface<T> {
	
    }
    
    public class GenericSuperclass<T> {
	
    }
    
    public class MyGenericClass extends GenericSuperclass<Float> implements GenericInterface<Long> {
	
	private GenericInterface<Integer> genericField;
	
	public GenericInterface<String> genericMethodReturn() {
	    return new GenericInterface<String>() {};
	}
	
	public void genericMethodParameter(GenericInterface<Double> genericArgument) {
	    
	}
	
    }
    
}