almost got all test cases

src/main/java/com/zipcodewilmington/assessment1/Cat.java

@@ -9,20 +9,24 @@ public class Cat extends Pet {
      * @param age age of this Cat
      */
     public Cat(String name, Integer age) {
-
+        this.name = name;
+        this.age = age;
     }
 
     /**
      * @param age age of this Cat
      */
     public Cat(Integer age) {
+        this.age = age;
+        this.name = "Cat name";
     }
 
     /**
      * @param name name of this Cat
      */
     public Cat(String name) {
-
+        this.name = name;
+        this.age = 0;
     }
 
     /**
@@ -32,12 +36,14 @@ public Cat(String name) {
      * age is 0
      */
     public Cat() {
+        this.name = "Cat name";
+        this.age = 0;
     }
 
     /**
      * @return meow as a string
      */
     public String speak() {
-        return null;
+        return "Meow";
     }
 }

src/main/java/com/zipcodewilmington/assessment1/Dog.java

@@ -9,20 +9,24 @@ public class Dog extends Pet {
      * @param age age of this dog
      */
     public Dog(String name, Integer age) {
-
+        this.name = name;
+        this.age = age; 
     }
 
     /**
      * @param age age of this dog
      */
     public Dog(Integer age) {
+        this.age = age;
+        this.name = "Dog name";
     }
 
     /**
      * @param name name of this dog
      */
     public Dog(String name) {
-
+        this.name = name;
+        this.age = 0;
     }
 
     /**
@@ -32,12 +36,14 @@ public Dog(String name) {
      * age is 0
      */
     public Dog() {
+        this.age = 0;
+        this.name = "Dog name";
     }
 
     /**
      * @return bark as a string
      */
     public String speak() {
-        return null;
+        return "Bark";
     }
 }

src/main/java/com/zipcodewilmington/assessment1/Pet.java

@@ -7,55 +7,73 @@ public abstract class Pet implements Animal {
     /**
      * nullary constructor
      * by default, pet has age of 0; name of "";
+     *
      */
+        String name;
+        Integer age;
+        PetOwner owner;
+
     public Pet() {
+        name = "";
+        age = 0;
+        owner = null;
     }
 
     /**
      * @param name name of this pet
      */
-    public Pet(String name) {
+    public Pet(String nm) {
+        name = nm;
+        age = 0;
+        owner = null;
     }
 
 
     /**
      * @param age age of this pet
      */
-    public Pet(int age) {
+    public Pet(int ag) {
+        name = "";
+        age = ag;
+        owner = null;
     }
 
     /**
      * @param name name of this pet
      * @param age age of this pet
      */
-    public Pet(String name, int age) {
+    public Pet(String nm, int ag) {
+        name = nm;
+        age = ag;
+        owner = null;
     }
 
     /**
      * @return name of this pet
      */
     public String getName() {
-        return null;
+        return name;
     }
 
     /**
      * @return age of this pet
      */
     public Integer getAge() {
-        return null;
+        return age;
     }
 
     /**
      * @param newPetOwner the new owner of this pet
      * ensure this instance of `Pet` is added to the owner's composite `pets` list
      */
     public void setOwner(PetOwner newPetOwner) {
+        owner = newPetOwner;
     }
 
     /**
      * @return PetOwner object whose composite `pets` collection contains this Pet instance
      */
     public PetOwner getOwner() {
-        return null;
+        return owner;
     }
 }

src/main/java/com/zipcodewilmington/assessment1/PetOwner.java

@@ -1,42 +1,60 @@
 package com.zipcodewilmington.assessment1;
 
+import java.lang.reflect.Array;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
 /**
  * Created by leon on 2/16/18.
  */
 public class PetOwner {
+
+    String ownerName;
+    List<Pet> ownerpets;
     /**
      * @param name name of the owner of the Pet
      * @param pets array of Pet object
      */
     public PetOwner(String name, Pet... pets) {
+        ownerName = name;
+        ownerpets = Arrays.asList(pets);
     }
 
     /**
      * @param pet pet to be added to the composite collection of Pets
      */
     public void addPet(Pet pet) {
+        ownerpets.add(pet);
     }
 
     /**
      * @param pet pet to be removed from the composite collection Pets
      */
     public void removePet(Pet pet) {
-
+        ownerpets.remove(pet);
     }
 
     /**
      * @param pet pet to evaluate ownership of
      * @return true if I own this pet
      */
     public Boolean isOwnerOf(Pet pet) {
-        return null;
+        return ownerpets.contains(pet);
     }
 
     /**
      * @return the age of the Pet object whose age field is the lowest amongst all Pets in this class
      */
     public Integer getYoungetPetAge() {
-        return null;
+        int youngest = ownerpets.get(0).getAge();
+
+        for(int i = 0; i < ownerpets.size();i++){
+            if(ownerpets.get(i).getAge()<youngest)
+                youngest = ownerpets.get(i).getAge();
+        }
+
+        return youngest;
     }
 
 
@@ -46,35 +64,48 @@ public Integer getYoungetPetAge() {
      * @return the age of the Pet object whose age field is the highest amongst all Pets in this class
      */
     public Integer getOldestPetAge() {
-        return null;
+        int oldest = ownerpets.get(0).getAge();
+
+        for(int i = 0; i < ownerpets.size();i++){
+            if(ownerpets.get(i).getAge()>oldest)
+                oldest = ownerpets.get(i).getAge();
+        }
+
+        return oldest;
     }
 
 
     /**
      * @return the sum of ages of Pet objects stored in this class divided by the number of Pet object
      */
     public Float getAveragePetAge() {
-        return null;
+        float totalAge = 0;
+
+        for(int i = 0; i < ownerpets.size();i++){
+            totalAge+=ownerpets.get(i).getAge();
+        }
+
+        return totalAge/ownerpets.size();
     }
 
     /**
      * @return the number of Pet objects stored in this class
      */
     public Integer getNumberOfPets() {
-        return null;
+        return ownerpets.size();
     }
 
     /**
      * @return the name property of the Pet
      */
     public String getName() {
-        return null;
+        return ownerName;
     }
 
     /**
      * @return array representation of animals owned by this PetOwner
      */
     public Pet[] getPets() {
-        return null;
+        return ownerpets.toArray(new Pet[0]);
     }
 }