Jackson polymorphic serialization/deserialization

import com.fasterxml.jackson.annotation.JsonSubTypes;
import com.fasterxml.jackson.annotation.JsonTypeInfo;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import org.junit.Assert;

public class TestSerialization {

    @JsonTypeInfo( use=JsonTypeInfo.Id.CLASS)
    @JsonSubTypes({ @JsonSubTypes.Type(value = AImpl1.class), @JsonSubTypes.Type(value = AImpl2.class)})
    public static interface A {
        public String foo();
    }

    public static class AImpl1 implements A {
        String s;

        public AImpl1(){};

        public AImpl1(String s){
            this.s = s;
        }
        public String getS() {
            return s;
        }
        public void setS(String s) {
            this.s = s;
        }

        public String foo() {
            return s;
        }
        @Override public boolean equals(Object o) {
            if (this == o)
                return true;
            if (o == null || getClass() != o.getClass())
                return false;
            AImpl1 aImpl1 = (AImpl1) o;
            return !(s != null ? !s.equals(aImpl1.s) : aImpl1.s != null);

        }
    }

    public static class AImpl2 implements A {
        int i;

        public AImpl2(){};

        public AImpl2(int i) {
            this.i = i;
        }
        public int getI() {
            return i;
        }
        public void setI(int i) {
            this.i = i;
        }
        public String foo() {
            return Integer.toString(i);
        }
        @Override public boolean equals(Object o) {
            if (this == o)
                return true;
            if (o == null || getClass() != o.getClass())
                return false;

            AImpl2 aImpl2 = (AImpl2) o;

            return i == aImpl2.i;

        }
    }

    @JsonTypeInfo( use=JsonTypeInfo.Id.CLASS)
    @JsonSubTypes({ @JsonSubTypes.Type(value = BImpl.class)})
    public static interface B {
    }

    public static class BImpl implements B {
        A a;

        public BImpl(){};

        public BImpl(A a) {
            this.a = a;
        }
        public A getA() {
            return a;
        }
        public void setA(A a) {
            this.a = a;
        }
        @Override public boolean equals(Object o) {
            if (this == o)
                return true;
            if (o == null || getClass() != o.getClass())
                return false;

            BImpl b = (BImpl) o;

            return !(a != null ? !a.equals(b.a) : b.a != null);

        }
    }

    @org.junit.Test
    public void testSerialisation() throws Exception {
        ObjectMapper objectMapper = new ObjectMapper();
        objectMapper.disable(SerializationFeature.FAIL_ON_EMPTY_BEANS);
        A a1 = new AImpl1("ggfd");
        A a2 = new AImpl2(5);
        B b1 = new BImpl(a1);
        B b2 = new BImpl(a2);
        String s1 = objectMapper.writeValueAsString(b1);
        String s2 = objectMapper.writeValueAsString(b2);
        B serializedB1 = objectMapper.readValue(s1, B.class);
        B serializedB2 = objectMapper.readValue(s2, B.class);
        Assert.assertEquals(b1, serializedB1);
        Assert.assertEquals(b2, serializedB2);
    }
}