allergies: Add test case to check when not allergic to anything similar to the python track.

allergies/src/test/java/AllergiesTest.java

 public class AllergiesTest {
 
     @Test
+    public void noAllergiesMeansNotAllergicToAnything() {
+        Allergies allergies = new Allergies(0);
+
+        assertEquals(false, allergies.isAllergicTo(Allergen.EGGS));
+        assertEquals(false, allergies.isAllergicTo(Allergen.PEANUTS));
+        assertEquals(false, allergies.isAllergicTo(Allergen.STRAWBERRIES));
+        assertEquals(false, allergies.isAllergicTo(Allergen.CATS));
+    }
+
+    @Test
     public void allergicToEggs() {
         Allergies allergies = new Allergies(1);